I’m not sure how Celeste does it specifically, but I think the important part is just being able to jump for a few extra frames after leaving a surface. I’d try it both ways and just go with whichever feels better.

My gut feeling is that gravity off will feel better, because it keeps your max jump height the same as it would be if you jumped before coyote time. It keeps things more predictable. Gravity on will mean that the max height gets slightly lower for each frame of coyote time before the jump starts.