The wait after installation and sealing grout depends on the products used and varies from a day to several weeks. You need to read the instructions carefully.
An enhancing sealer, unless it is left to dry on an impervious surface, basically is permanent. It is absorbed, and is designed to darken things that can absorb it. If it wasn't absorbed by the tile, you might get it off of it with a solvent, but if it was an unglazed tile (except maybe a good porcelain), it won't come off.