It surprises me how many of you don't know this- or the amount of you that think this game takes "great reaction time".

It's not a bug, the game is turn based with wiggle room, everyone has a "Turn" each position takes their turn depending on their position & initiative- for some reason before the update there was a "Delay" before every action was committed, almost as if the game added it's own "breathing room delay"(Including queueing up a mystery), the only time this isn't the case is just before the standard attack of a Ninja, there seems to be a "Clear Opening" where it will instantly queue the mystery & activate it because "it's that ninjas turn", so for example Normal Gaara- if you used his mystery EXACTLY in the window just before his standard, he would instantly cast his barrier
(this is still the case btw, I've never had my Gaaras barrier cancelled by an interrupt, it's impossible. It's only possible in teamplay due to not being able to accurately account for everyone's turn)- not really a bug, more a symptom of the system in place.

That system still exists but all delays have been taken out, even the delay when you queue'd up a mystery, so much so that it has made even things like team play & GNW significantly faster- I think they've done it by not trying to sync the players together as heavily & probably just a cleaner construction on the back end- or maybe the game did deliberately add the "Delay" before every action.

This in turn is why you can't interrupt other peoples mystery as in most cases, assuming you don't use your mysteries exactly when another Ninja is taking an 'Action' such as during a chase, or even during the "Heal" animation on a healer, it will just instantly cast the mystery- you click it, it uses it assuming no one else is taking an action.

The only time I've found this not to be the case is against players with much lower ping, some times they are just ahead enough to instantly click & cancel an ability with an interrupt as if there's a delay on my end created due to latency but it's super rare & is only accounted for due to me playing on US servers when I'm in the UK.
Generally speaking though, no one on this earth can ever cancel one of my mysteries if I use it correctly- you don't have godly reaction time, you just can't beat how the game is set up mechanically.- The only time this isn't the case is if you know about this mechanic & know I will use Gaara just before his standard attack, in which case you're waiting for the same thing- using your mystery just before my standard.

The best time to use an interrupt is by trying to gauge when they will actively click it- A good example is with Water Main blitz, when Mabui takes an 'Action', for example the "Heal" on her turn, she gains chakra- if you wait for that "Heal" people generally instantly click Tenten as soon as they get that chakra, wait for Mabui's "Action" then use your mystery & they should queue up Tentens, of course people know this & just don't queue it, which is why the ninjas that interrupt aren't that great.
This is also an "If they're using Water Main blitz", generally you just can't anticipate when they'll use a mystery,