The grout dried for about a month and a half, but that was while I was waiting for the sealer. If I had the sealer on hand I would've probably given it a week or so.
This is what I used:
Waterproof Sealer for wood,masonry,roofs,metal

The fluorite is the aquatic substrate, as this tank also houses white cloud minnows and red cherry shrimp.
Although for my next project I intend on mixing the aquatic substrate in with the grout, this way the theme is consistent throughout.