I let the decals set for at least 24 hours. If the last decal I applied hasn't had the final quick coat of Solvaset applied, I do that first, and then wait another 24 hours. After that, it is time to apply a single spray coat of Testors Dullcote to the whole model. This removes the sheen from the Glosscote and adds a protective layer to both the paint layer and the decals.
(external link: Testors Dullcote)