The building empties in two stages
Administrative staff in an education provider usually finish at a conventional hour while teaching continues for several more. That produces two distinct windows rather than one, and treating them separately is what makes the schedule workable. The administration floor, staff room and offices can be serviced from early evening while classes are still running elsewhere in the building.
Student-facing areas follow later in the evening. Classrooms, the student lounge, reception and the washrooms used by students all have to wait until the last class has finished and the floor has cleared. Because that is a fixed and published point in the timetable rather than an estimate, it can be scheduled precisely, which is a considerable advantage over premises where the finishing time varies from night to night.
