If the clear has not been done in an oven you might want to be vary wary of the thinners in the coat you apply reacting with the coat on the car.
If you break its "skin" while sanding, this will be a sure thing and nasty things may well happen.
Any time I've had to leave a job till the AM I've just blown the area off with the air line, then applied a "wet coat" to key into the already very soft area, then dusted a few more coats on top. Have to make sure it has flashed very well though.
Another thing to take into account any sanding that you do to a clear coat will show through under the layers you apply next.
Either way, be very wary of thinners reacting with the paint you have on the car already.
Good luck m8.