We do this, and X == 150. We could always increase that value if it makes sense. Note that we don't wait if the user presses tab twice.

Timing is tricky here since everyone alt-tabs at slightly different speeds (which we've learned from trying out different paradigms), but we should can try increasing the value a bit to start and see how it feels (understanding that this may then open complaints that it's too slow :). 

Let's try increasing X to 225ms (a suggested value from Material animations) to start.
(https://material.googleplex.com/motion/duration-easing.html#duration-easing-common-durations for reference).

I also wonder if we can do something with the timing of the black background and have it appear after the previews animate in. +sgabriel as well for his thoughts here. 

I agree on trying 225ms to see how it feels, but I'm guessing there's a fine line between a functional timing a something that feels too slow.

Regarding making previews appears before black scrim, it will certainly make the flashing lighter, but still present considering the size of our previews and it will probably make it feel more buggy (flashing small windows on top of big windows).

I think this has been fixed in another bug.
Current implementation of alt-tab is working as intended as far as I know.

9270.0.0/58.0.3007.0