Did mine at Oxford (as CBG is closed at weekends....grrrr) which is open till 22:30 (local) seven days, but often open later as they can open till midnight. If staying over, lots of cheap hotels very close and Enterprise-Rent-a-Car on site do £14.95/day for car hire over weekends. They did several circuits and landings with parking for a fair flat fee around £100 - just call their operations.