Quote Originally Posted by radja View Post
you can spend an action point at the start of your turn, at the end or any other time during your turn.
It's slightly incorrect.

You cannot Spend an Action point at the start of your turn or at the end of your turn because you cannot take actions during these phases, only during your turn phase because Spending an Action Point is a free action.

Suppose a game element was giving a Warden a bonus to saving throws, he wouldn't be able to Spend an Action and benefit from this bonus while making a save with Font of Life for exemple.

A more accurate way of putting it would be to say that you can Spend an Action at anytime during your turn.

RC 197 No Action: A creature can't take actions at the start of its turn.