The Room of Silence in the Mensa building is generally open during the opening hours of the A_KAFFEE. The opening hours can be found on the AKAFÖ website under Opening hours → Ruhr-Universität Bochum.
The location in the GB building is open Monday through Friday from 12:30 p.m. to 6:30 p.m. Further information can be found on the AStA website (German website).