There are many variables in the timing of resin cure with both polyester and epoxy resins (temperature, humidity, type of resin, etc) so it's better not to rush and just make sure the lamination is hard.
Note: Polyester resin will still be a bit tacky after curing... you can still sand it but make sure the resin is cured and stiff.
Epoxy resin will be nice and hard and sand easily