!st ed: The Summon Monster and Summon Nature's ally spells all have a casting time of 1 round. My regular group have always taken that to mean that the summoned creature begins to act in the following round. My new group (I'm GM for the first time) is claiming that it should appear and start to act in the round in which the spell is cast. Who is right? Does it make any difference if the caster is actually a Preservationist Alchemist invoking Bottled Ally?
The rules for casting time state that 1 round casts cannot take effect the same turn as the action spent casting them (from CRB p. 213):
A spell that takes 1 round to cast is a full-round action. It comes into effect just before the beginning of your turn in the round after you began casting the spell. You then act normally after the spell is completed.
Unfortunately, there appears to be some ambiguity with Preservationist alchemists. It's stated that it takes a standard action to "draw and drink" an extract, but it's not clear whether this can be generalized to extracts that are not drunk. The Preservationist itself does not provide any details on the time it takes for its summons to take effect. From a meta standpoint, the ability to summon as a standard action is a major part of what makes other summoning builds useful and fun to play, so I would lean towards allowing a Preservationist to use the faster option since it's presumably going to be a primary strategy for them.