How long is too long?

[mudkipmaster]

Azelf, Mespirit, and Uxie all have powers that can be used "when you play them from your hand" How long would I have to decide to use the power? (Would I have to play one of them and then call the power immediately or do I have some thinking time after I play the card down before I make another move?)

 

[PokePop]

You have a little thinking time, but really, why not think before you put it down?
Bottom line, though, if you advance the game state by doing something else before declaring the Power, you have missed your chance.