Invisible Fist interrupting an attack?

[SangoProduction]

I got a monk with Invisible Fist. Says you can activate invisibility as an immediate action. This would mean that you could force someone who just rolled successfully to now have to beat the miss chance invisibility imparts?

[StreamOfTheSky]

I'd think you'd have to use it before they hit you.

That said, I play online and it's often pretty unrealistic to shout out, "I use [insert immediate action defense here]!" before the roll is made (usually we declare what the attack is in the same message that has the roll), and it'd massively slow the game down to give some time between each declared attack to wait for people to pipe up, so IME it may as well be after a hit has been determined, practically speaking.

I have a monk w/ it right now, and due to the above reasoning, DM is cool w/ me declaring it after the roll's been made.

Spoiler: My favorite use so far

Show

Sprang a trap w/ an attack roll (falling rocks). I wasn't flatfooted, so I used my immediate action on invisible fist and the rocks went from hitting me to missing. It was silly, I don't think the rocks can "see" me either way, but it worked.

[Necroticplague]

Not quiet. You can do an immediate reaction as a reaction to an event, which then occurs before the trigger (solving under standard first-in-last-out logic). However, if the attack roll has occurred, then the attack has already occured, then it's too late. The attack roll and damage roll are one and the same process (both being the resolution of the attack action). So you couldn't use it to add a miss chance to an attack that already hit, but you could react to an attack to by turning invisible, taking a miss chance onto it.