For the Star Trek Hunter series, the U.S.S. Hunter has four duty stations that must be staffed at all times - Command and Ops on the bridge, Ops in engineering and Transporter Room 1. With a crew of 35 (+3 holographic warrant officers), the Hunter is on a 3-shift rotation, but only the A shift is fully staffed.
Ground Operations is responsible for staffing Ops, but any qualified crew member can staff that position. Similarly, the Engineering Department is responsible for staffing Ops in engineering and TR1, but any qualified crew member can stand watch. Any qualified officer can staff Command, but that's typically Executive Staff and the Flight Operations officers. All crew members cross train to maintain qualifications and typically trade off 4-hour half shifts at required stations for peak training and readiness. All officers from ensign up maintain Command qualification. The COO (2nd officer) is responsible for scheduling. The XO (1st officer) is responsible for training and qualifications, but this flows through the command structure for each department.
Typically, at least one Flight Ops crew member is on watch in the shuttle/intercepter bays, at least one of the Medical staff is on watch in Medical and at least 2 members of the Engineering staff are in engineering. Ground Operations is staffed as needed. Other than the 4 critical stations, staff rotate in and out as needed and when not needed (which is most of the time), their schedules are heavily geared toward training. The Hunter's mission profile requires all crew, particularly flight and ground operations, to be in peak physical and mental condition, highly prepared for complex tactical situations and ready to respond at a moment's notice.