If I may add everyone's information together:
So, Jimmy, you have a free action to use!
Yes sir, Mr. Rules!
First off, is this a free action attack?
If NO go to ABLE TO USE
Yup!
Have you used a Free Action attack this turn yet?
if NO go to ABLE TO USE
Yes, actually.
Sorry, Jimmy. You can only do that once a turn! END
ABLE TO USE
Well, Jimmy, is it a Triggered action?
If yes goto TRIGGERED else go to UNTRIGGERED
TRIGGERED
Why, sure it is, Mr. Rules!
Well then, if it were not an interrupt, could the power work at all?
If yes goto REACTION, else goto INTERRUPT
REACTION
It'd work just fine, but if I used it before it could negate-
Sorry, Jimmy. Your power goes at REACTION speed. END
INTERRUPT
I think not, Mr. Rules! If I don't I won't be able to re-roll the attack at all!
Well then Jimmy, you're in luck! It goes off at INTERRUPT speed! END
UNTRIGGERED
Nope, it just targets, or isn't even really a reactionary power!
Well then, judging by the ruling for Warden's ability as well as things like "Speak a few sentences", you can do it at any time! It doesn't turn back the clock like an Interrupt, but can happen in the middle of anything in the game, assuming there's actually a middle for it to happen in. You can do it in the middle of a move, while swinging your sword, or even while being pummelled by that troll! Of course, the rules are vauge on these points, and it could be true that you can only use the power on alternate thursdays, but there ain't no rule saying you have to, so if you want to use your free action to let a monkey play professional tennis in a horrible feel-good family film, then that's your choice.
Uh, you mentioned a troll?
Oh, don't worry about him. He's probably not that hungry. oh, wait, yes he is. See you later, Jimmy!
Wait, Mr. Rules I -.... um. So uh, Mr. Troll.. ... gulp. END