How Long to Let Decals Dry Before Clear Coat - Model Railroader Magazine

Good tips mentioned above. There are talented modelers on this forum that have performed stunning "manufacturer grade" decal work and, to me, it's enjoyable seeing their photos (especially Doc Wayne).

I would like to respectfully add a tip that might be helpful in some cases.

After applying decals, allow them to fully adhere to the surface. Afterwards, instead of immediately applying dull coat or a flat clear, apply one thin even coat of a gloss or semi-gloss clear. Allow it to cure.  Follow up with one to two coats of flat clear (or dull coat for those that use it).  I've found that this does a decent job of hiding decal film edges well, especially on metallic and darker toned colors  (ie: Black locomotives with light colored decals, such as Penn Central, Norfolk Southern, Atlantic Coast Line and metalized passenger cars with a weathered look).

I usually do that extra step for some models that I want to make "stand out" or that I plan on taking photos of that will be posted on a forum.