Enlarge effects, next turn?

[Kurald Galain]

I've met several GMs who claim that any effect that works like Enlarge Person (such as the Growth subdomain, the Abyssal bloodrager bloodline, and possibly a potion of Enlarge) takes effect one turn after activating it, because the Enlarge Person spell takes effect one turn after you start casting it.

Is this stated in the rules or FAQs anywhere? Or is perhaps the opposite stated in rules or FAQ? Is this perhaps a reaction to a particular cheese build that I'm unaware of?

[vhok]

enlarge takes place 1 round later because its a 1round cast time, other effects take place depending on the activation time.

the 1 round later is from the cast time and has nothing to do with the enlarge effect

growth subdoman is a swift so it happens instantly, bloodrager bloodline happens as soon as you begin a rage(if you wish it to it is a may)

anyone that says otherwise is wrong.

[Balacertar]

The enlarge person spell works next round because spells with 1 round casting time are completed at the beginning of your next round.

If the abilities you are referring to do not state what actions they require to use them but just say they work like the spell, then you have to look at what is the default way abilities work.

Spell-like abilities (Sp): "A spell-like ability has a casting time of 1 standard action unless noted otherwise in the ability or spell description. In all other ways, a spell-like ability functions just like a spell." Hence they work like the enlarge person spell and enter into effect the next round unless noted otherwise.

Supernatural abilities (Su): Nothing is said as to what action is to activate one of these. The text must include this information.

Potions: "Drinking a potion or using an oil is a standard action. The potion or oil takes effect immediately." Hence drinking a enlarge person potion is just a standard action and you are instantly enlarged, no need to wait for the next round.

Scrolls: "Activating a scroll is a standard action (or the spell's casting time, whichever is longer) and it provokes attacks of opportunity exactly as casting a spell does." Hence casting from a scroll just works like casting the spell.

Thus, answering your examples:
Growth subdomain: The enlarge is a supernatural ability, thus the text just describes how it works the enlarge happens just immediately because the ability states it is a swift action to activate. Even if this was a spell-like it would work the same.
Abyssal bloodrager bloodline: The demonic bulk is a supernatural ability, and its texts states "when entering a bloodrage", thus you can make this to happen automatically when you start a bloodrage and thus governed by the time you need to enter a bloodrage (a free action normally).
Potion: Because potions take effect immediately, this is a standard action and takes effect that same round.

One can argue about the balance of this and complain about the spread of the base rules and clarity of supernatural abilities, but the rules are there.

[MrCharisma]

Yeah I've had a few characters buy potions of Enlarge Person specifically to avoid the 1-round casting time for a spell/wand/scroll, but if you have a class ability that does it they're often quicker.

[Agénor]

In case it is relevant, the fifth level Cleric spell Righteous Might increases the caster's Size by one among other effects while taking a Standard Action to cast.

[*Khan*]

If you are using growth subdomain be aware that the enlarge effect only last a round. So you need to use a swift action again the next round.
It also have an advantage of a free tactical movement as you choose which squares you enlarge into and which reduce into after the round.