Neither law nor applicable guidance abrogates the discretion to work AUO to the individual employee. In other words, let’s say you are working a group past your shift. Can a supervisor tell you to disengage and return to the station to go home? The answer is an unequivocal yes.
hours of work employees are assigned is a condition of employment subject to negotiation; a mandatory topic of negotiations. Immigration and Naturalization Service, (FLRA 1995).