On the grillz question, yes, they come out. Anything that is not a natural part of your body gets surrendered during the intake and booking process before you are assigned to permanent housing. That includes grillz, hair extensions, wigs, toupees, and similar items. The facility holds them with your other personal property, and in most cases you get them back upon release. Permanent grillz that are genuinely fixed to the teeth are a gray area that gets handled on a case by case basis, but the default position of most facilities is that anything removable gets removed.
On sleep, the schedule varies by facility but the general framework in most jails and prisons runs something like this. Lights out is typically between 10pm and 11 pm, depending on the unit and the facility. Inmates are usually woken up between 5am and 6am for count and breakfast. That works out to roughly six to eight hours of sleep time on paper, though how well anyone actually sleeps in a dormitory or cell with multiple people, ambient noise, regular count checks throughout the night, and the general stress of the environment is a different question entirely.
Federal facilities and state prisons tend to have more structured schedules than county jails, where the routine can be less predictable. Some facilities have quiet hours that are enforced more strictly than others. The bottom line is that the opportunity for a full night of sleep exists within the schedule, but the environment does not always cooperate.