How long do I have to wait for the tile grout to cure before I can seal it ?

you can't seal the porcelain tiles so when you seal the grout you can use a sponge to seal it faster

and later you can easily clean the excess haze off the tiles

there is a epoxy grout that you can use and u don' t have to seal

I usually seal the grout on the next day but if you still have the bag from the grout look there

for the manufacturers recommendations

3 days minimum. Wait a week if you can.