Ok, I was looking at the planar binding rules, because I've reached a level where it could be available and useful. I noticed that:
Planar Binding, Lesser:
Source PRPG Core Rulebook pg. 321
School conjuration (calling) [see text]; Level arcanist 5, medium 4, occultist 5, psychic 5, sorcerer 5, summoner 4, summoner (unchained) 5, wizard 5
Casting
Casting Time 10 minutes
Components V, S
Effect
Range close (25 ft. + 5 ft./2 levels)
Target one elemental or outsider with 6 HD or less
Duration instantaneous
Saving Throw Will negates; Spell Resistance no and yes; see text
Description
Casting this spell attempts a dangerous act: to lure a creature from another plane to a specifically prepared trap, which must lie within the spell's range. The called creature is held in the trap until it agrees to perform one service in return for its freedom.
To create the trap, you must use a magic circle spell, focused inward. The kind of creature to be bound must be known and stated. If you wish to call a specific individual, you must use that individual's proper name in casting the spell.
The target creature is allowed a Will saving throw. If the saving throw succeeds, the creature resists the spell. If the saving throw fails, the creature is immediately drawn to the trap (spell resistance does not keep it from being called). The creature can escape from the trap by successfully pitting its spell resistance against your caster level check, by dimensional travel, or with a successful Charisma check (DC 15 + 1/2 your caster level + your Charisma modifier). It can try each method once per day. If it breaks loose, it can flee or attack you. A dimensional anchor cast on the creature prevents its escape via dimensional travel. You can also employ a calling diagram (see magic circle against evil) to make the trap more secure.
If the creature does not break free of the trap, you can keep it bound for as long as you dare. You can attempt to compel the creature to perform a service by describing the service and perhaps offering some sort of reward. You make a Charisma check opposed by the creature's Charisma check. The check is assigned a bonus of +0 to +6 based on the nature of the service and the reward. If the creature wins the opposed check, it refuses service. New offers, bribes, and the like can be made or the old ones reoffered every 24 hours. This process can be repeated until the creature promises to serve, until it breaks free, or until you decide to get rid of it by means of some other spell. Impossible demands or unreasonable commands are never agreed to. If you ever roll a natural 1 on the Charisma check, the creature breaks free of the spell's effect and can escape or attack you.
Once the requested service is completed, the creature need only to inform you to be instantly sent back whence it came. The creature might later seek revenge. If you assign some open-ended task that the creature cannot complete through its own actions, the spell remains in effect for a maximum of 1 day per caster level, and the creature gains an immediate chance to break free (with the same chance to resist as when it was trapped). Note that a clever recipient can subvert some instructions.
When you use a calling spell to call an air, chaotic, earth, evil, fire, good, lawful, or water creature, it is a spell of that type.
Ok, a) note the casting time, and b) you must use a magic circle spell (or equivalent) to make the trap.
Then look at
Magic Circle against Evil:
Source PRPG Core Rulebook pg. 308
School abjuration [good]; Level arcanist 3, cleric 3, inquisitor 3, medium 3, occultist 3, oracle 3, paladin 3, shaman 3, sorcerer 3, spiritualist 3, summoner 3, summoner (unchained) 3, warpriest 3, wizard 3
Casting
Casting Time 1 standard action
Components V, S, M/DF (a 3-ft.-diameter circle of powdered silver)
Effect
Range touch
Area 10-ft.-radius emanation from touched creature
Duration 10 min./level
Saving Throw Will negates (harmless); Spell Resistance no; see text
Description
All creatures within the area gain the effects of a protection from evil spell, and evil summoned creatures cannot enter the area either. Creatures in the area, or who later enter the area, receive only one attempt to suppress effects that are controlling them. If successful, such effects are suppressed as long as they remain in the area. Creatures that leave the area and come back are not protected. You must overcome a creature's spell resistance in order to keep it at bay (as in the third function of protection from evil), but the deflection and resistance bonuses and the protection from mental control apply regardless of enemies' spell resistance.
This spell has an alternative version that you may choose when casting it. A magic circle against evil can be focused inward rather than outward. When focused inward, the spell binds a nongood called creature (such as those called by the lesser planar binding, planar binding, and greater planar binding spells) for a maximum of 24 hours per caster level, provided that you cast the spell that calls the creature within 1 round of casting the magic circle. The creature cannot cross the circle's boundaries. If a creature too large to fit into the spell's area is the subject of the spell, the spell acts as a normal protection from evil spell for that creature only.
A magic circle leaves much to be desired as a trap. If the circle of powdered silver laid down in the process of spellcasting is broken, the effect immediately ends. The trapped creature can do nothing that disturbs the circle, directly or indirectly, but other creatures can. If the called creature has spell resistance, it can test the trap once a day. If you fail to overcome its spell resistance, the creature breaks free, destroying the circle. A creature capable of any form of dimensional travel (astral projection, blink, dimension door, etherealness, gate, plane shift, shadow walk, teleport, and similar abilities) can simply leave the circle through such means. You can prevent the creature's extradimensional escape by casting a dimensional anchor spell on it, but you must cast the spell before the creature acts. If you are successful, the anchor effect lasts as long as the magic circle does. The creature cannot reach across the magic circle, but its ranged attacks (ranged weapons, spells, magical abilities, and the like) can. The creature can attack any target it can reach with its ranged attacks except for the circle itself.
You can add a special diagram (a two-dimensional bounded figure with no gaps along its circumference, augmented with various magical sigils) to make the magic circle more secure. Drawing the diagram by hand takes 10 minutes and requires a DC 20 Spellcraft check. You do not know the result of this check. If the check fails, the diagram is ineffective. You can take 10 when drawing the diagram if you are under no particular time pressure to complete the task. This task also takes 10 full minutes. If time is no factor at all, and you devote 3 hours and 20 minutes to the task, you can take 20.
A successful diagram allows you to cast a dimensional anchor spell on the magic circle during the round before casting any summoning spell. The anchor holds any called creatures in the magic circle for 24 hours per caster level. A creature cannot use its spell resistance against a magic circle prepared with a diagram, and none of its abilities or attacks can cross the diagram. If the creature tries a Charisma check to break free of the trap (see the lesser planar binding spell), the DC increases by 5. The creature is immediately released if anything disturbs the diagram—even a straw laid across it. The creature itself cannot disturb the diagram either directly or indirectly, as noted above.
This spell is not cumulative with protection from evil and vice versa.
How are you supposed to cast a 10 minute spell in the round after you cast magic circle? Even if you say start casting (rather than complete casting in the round after you cast the magic circle), how are your supposed to get the Dimensional Anchor in, quicken it?
Interesting argument. For several effects what matter is the moment in which you start casting (counterspelling, provoking an AoO), so I would rule that what matter is starting the spell the next round, not completing it.
More RAI than RAW, but I think we only need to rationalize how it works as RAI is clear.
For Dimensional anchor, the summoning spell will complete just before the beginning of the summoner turn, so he has the time to cast it. That way you satisfy the first way to use it ("You can prevent the creature's extradimensional escape by casting a dimensional anchor spell on it, but you must cast the spell before the creature acts.")
For the second condition ("A successful diagram allows you to cast a dimensional anchor spell on the magic circle during the round before casting any summoning spell.") it seems you need to quicken one of the two spells.
Almost certainly the whole part about needing to cast magic circle the round before casting the summoning is a leftover from an older version of the text.
Would you give the caster a surprise round to get his dimensional anchor in?
No, but ou act before the called creature unless it has your exact initiative and a higher initiative bonus.
The turn sequence has already started, so if it has a higher round initiative its turn has already passed, if it has a lower initiative it acts after you.
To go back to the first edition of AD&D, in one of the supplements it was said that the summoning spell appears as an enticing object on the plane of the summoned creature and that the creature is fascinated by it and is summoned when it touches it. I don't recall a recent book explaining how it works from the point of view of the summoned creature, but we can assume that it isn't forewarned unless it is something very powerful that has prepared in advance some defense, so he will in the same situation as someone entering a turn-based event when it has already started. Not surprised, not flat-footed, but unable to take non reactive actions until its turn came out.
The Planar Binding spells are kind of a mess. Diego suggested it's a holdover from an older edition. It's also possible that someone had Planar Binding confused with summoning spells. There's indirect evidence that this was a problem for a while in the first year or two of PF1e. (See, for instance, the language about "before casting any summoning spell".)
Whatever the reason, the Planar Binding spells are just... badly written. Most of the 1e core books are VERY clear and consistent, so it's actually kind of shocking how badly they fall down here. This is a known problem; I have some discussion of it in my Guide to Planar Binding, which can be found here (along with a bunch of other stuff).
Anyway: the best way to work is to apply the Rule of Cool and just say, okay, you prep Magic Circle and Dimension Anchor, draw your circle, and cast those two plus Planar Binding and off you go. This makes perfect thematic sense and is not OP; you're spending time, spending resources, and you can't eliminate that 5% chance of failure. And it is pretty close to RAW -- and, as noted, RAW is a hot mess here.
But if you want to be a stickler and stay as close to RAW as possible, then (1) draw your circle, and (2) cast Dimension Anchor. And then (3) you immediately (within one round) start the 10-minute casting of Planar Binding. And also (4) in the same round as you do that, you cast the inward-facing circle as a Quickened spell so that you get it off in that same silly one-round window. That's kind of dumb and tedious, but it would seem to satisfy the badly-written spell description. If you get a real rules lawyer as DM he might argue that the RAW says "cast the spell [Planar Binding] within one round", not BEGIN to cast the (ten-minute casting time) spell within one round, but at that point we're really into eyeroll territory IMO.
...of course, in 2nd Edition, Planar Binding has been nerfed down into a slightly overcomplicated version of Planar Ally. I don't even know why they kept the name; there's no binding, just calling an extraplanar creature to negotiate payment and service.
I'm not a 2e hater. But I think they really chickened out on this one. Planar Binding in 1e is a flawed, kludgey mess, but it generates all kinds of cool and crazy game ideas and plot seeds.
