On most catalyzed enamel systems, you only need to allow a certain flash time, then apply the clear, no sanding of the base coat is necessary , it's not really a good thing and should be avoided.
If you just did it, just use a tack cloth on the base and spray your clear. I wouldn't let it go for too long though, before you clear it. The rule in general is 24 hours or less (again, some paint types/systems are different , some are more open-ended), so do it asap.
