I put down 12 x 12 porcelain floor tiles in a bathroom using mastic type 1. I walked on it after 9 hours and it's still squishy in places. Then I read the directions (I had used this same mastic before) and realized that up to 6 x 6 is recommended and that it could take much longer than 24 to 48 hours to dry). I wish I'd read the directions beforehand.
Can I wait until it dries and continue with the grout. I didn't realize there was such a difference in mastic and thin set.

Thisn set will cure even under water, mastic has to air dry by solvent evaporation. Ou are stuck now unless this is a small area you can pull up. Do you have another bathroom? This could take a week and even then not fully cure in the center of the tile. Walking on the tile before cure could move them but the bigger issue is the tiles can crack.