Sorry SE, but endgame won't work if you don't fix something.

[Astarica]

Atleast 50%? Man I get consistently to around 0.30-0.10 seconds left of full 1 second cast before it interrupts. In fact yesterday was abnormally laggy and I managed to actually run and mount without interrupt. Every now and then the run and mount caused a 90k.

I was doing that test while queueing up a level 45 dungeon as a DPS so I had a lot of time to test, and one time the spell actually interrupted at around 0.5s hence I said at least 50%. 0.3 to 0.1s left is the common case yes, and yeah I was able to finish casting the spell quite a few times too but nothing actually happened (which makes sense, since you shouldn't be able to do this at all).