This stress will be tensile during temperature decrease, or compressive. during temperature increase. If the compressive stress level exceeds the column buckling resistance of. the restrained length, then lateral buckling (or snaking) will occur.
Dry Time. In most cases, you should allow the grout to dry overnight before using that room as total dry time may take up to 24 hours. If you are thinking about sealing your grout after you have installed it, you need to wait even longer than that so that all of the moisture has had time to be released.
All you need to do is leave the grout to dry before getting it wet. The instructions should tell you for how long. As you and others have pointed out drying and curing are separate things. While you can use the shower after the grout is dried you may need to leave it for a day or two after it's cured before sealing.