Hi Jack, Welcome!
As Paul mentioned, wait a minimum of 72 hours before sealing the grout.
If you're starting with an enhancer, and you're happy with the grout color after it cures, you can use a non enhancing solvent based impregnating sealer concentrating on the grout, but can carry it over the enhanced stone. Be sure to not let any excess sealer dry on the surface.
I also suggest TESTing a spare tile first. You want to try to get a darker color grout to mesh with the enhanced color of the stone. It is rare to achieve desired results when enhancing grout.