One or two per map, the timer is either pre-set or set by the owners when they claim it. The window to claim on wipe might require constant attention/defending as people fight over it. after the monument is claimed, it becomes locked down and only the owners of the TC can open the door. It takes one minute to open the door and to close it outside of the 6 hour window.
Inside this buildable area there will be a static TC that cannot be broken but can be damaged/have lock destroyed.
During the 6 hour window, the door is open and anyone can attack or raid.
Maybe it should cost diesel or scrap to upkeep the safety features of this.