Full-round spells and AoE targeting

[Dazz]

Only recently realizing that Sleep is a full-round casting time, I'm wondering if this becomes a big issue and having been able to find the solution on the PRD. It has an effect area of "one or more living creatures within a 10 ft burst."

Do you need to decide the area it effects when you start casting, or when it comes into effect the next round?

Along the same lines, when you summon a creature (also full-round), when do you decide where it appears?

[Dolanar]

When the spell activates & when the monster appears. basically as you're casting you're also selecting the target & as you finish your final targeting decision is where it goes as far as I recall.

[Finkmilkana]

Full Round is not the same as 1 Round, it just means it uses both your actions.

[Adamantine Dragon]

For pretty much any spell you cast, you should just assume (unless otherwise stated in the spell description) that the very last thing you do is determine where it will go off.