Y need to wait ...

You are talking about drying time and cure time. Sure paint will dry in a few hours but may take several days to cure. By cure, that means the paint has dried through and through. Solvents can loosen the top layer of paint and attack the un cured part of the paint. Also by sealing the paint before it has a chance to cure causes the bottom layer to react and could cause peeling and an orange peel effect on the sealer.
Spraying the decals with a clear gloss will help protect the decal. It also seals it and if your model needs a flat finish you spray the flat on after the gloss has dried.

Berny

web_boy,
If you don't wait for the paint to 'cure' (ie several days with enamels), it stays 'soft' and you can actually get fingerprints or other muck in the paint. It's a big problem for me because I always convince myself that it's 'dry enough' to handle or work with, but sure enough I end up with a fingerprint or some other dent in the paint.
Different paints have different cure times, but the basic testors enamels take the longest (that I'm aware of...)

M.