Let's say your party Rogue comes across a secret door with a magical Summon Swarm trap guarding it and he doesn't find it before opening the door.
How long after tripping the trap does the swarm appear? Immediately, is the spell held in abeyance waiting to be let loose, or after a one round delay, like the spell is being cast as soon as the trap goes off?
Typically, it should just go off and trigger the spell. There might be instances or occasions when it might be delayed for intentional or specific reasons but, in general, the trap should just trigger.
The problem is that triggering means casting the spell. That means the spell comes into effect next round. Just about every other spell trap completes the action on the same round.
Thanks for your help. Upon further digging I found this in the Glyph of Warding spell description:
Spell Glyph: You can store any harmful spell of 3rd level or lower that you know. All level-dependent features of the spell are based on your caster level at the time of casting the glyph. If the spell has a target, it targets the intruder. If the spell has an area or an amorphous effect, the area or effect is centered on the intruder. If the spell summons creatures, they appear as close as possible to the intruder and attack. Saving throws and spell resistance operate as normal, except that the DC is based on the level of the spell stored in the glyph.
Which leads me to believe that the spell released is instantaneous.