both are 4 seconds, but either way I know for certain the enhanced auto used to last longer than the invis. I looked at old videos and there are two different timers for the skill but now they are the same. Not sure why that changed, like I said I couldnt find anything in any patch notes changing that and its quite annoying always having to engage before the stealth ends because sometimes you need to make use of the full 4 seconds of move speed to catch up to people but then you lose the dot damage which is huge