10. A few hours after you lay the grout down, sponge it off the tile areas with a decent sponge and bucket of warm water, smoothing the grout lines as you go.

Not enough time, and the grout will peel off with the sponge. Wait a little linger. Too much time, and you'll be at how hard you have to work to get it off. Follloing instructions is good, but over time you get a sense of when it's set up right and you can start sponging it.