Vayne's tumble gives 1s invis during ult, but doesn't proc duskblade. Why is this @_@

You need to wait for the invisibility to fall off to gain the effect of duskblade. If you auto before that, you won't get the proc.

It's probably not actually a full second on the code side. Also it could just be a bug.

because vayne is OP as it is. she isn't called queen of the tank meta for nothing.

I mean I see her tumble and she gets about .5-.75s of it from what I can tell. It isn't quite a second and I feel that is on purpose as she isn't supposed to be a heavy stealth champ it is meant for re-positioning.

Are you lasting out the duration? Because I know you're able to auto before the full second is up

You need to be unseen for 1 second before Duskblade's effect kicks in, and Vayne's invisibility lasts 1 second as well. In other words, you only get it AFTER the invisibility has expired.

And there is also the question on which action is executed first if both are done at the same time, which may affect whether or not it is even possible for Vayne to get the Duskblade effect; otherwise, the previous paragraph applies, you need to wait until the invisibility expires before you have access to its effect.

I just tested and found that you actually do get the duskblade proc if you wait for the invis to expire before you attack.

No surprise there. It lasts exactly 1 second so you have to wait until after it expires before you attack.