Three adult MAG.
168 hours per week / by 8 hours = 21 shifts per week
A person is assigned to one (8 hour) security shift per day, that same person would have 8 hours of finding/preparing food, relaxation, backup to the person on the security shift, communications, savaging, repairing, personal hygiene, scavenging, rebuilding, etc. and 8 hours to sleep.
Using the above stats the three people MAG could provide 24x7 security 7 days a week. Status quo can be maintained as long as no one is injured or sick. .
How alert do you think a security person would be after an extended period of time under this scenario?
Six adult MAG.
168 hours per week / by 4 hours = 42 shifts per week.
A person is assigned to one (4 hour) security shift per day. The same person would have 8 hours to find/plant harvest food, backup the person on the security shift (along with the other 2 persons not sleeping), communications, savaging, repairing, scavenging, rebuilding, etc., another 4 hours for personal free time (eating, relaxation, personal hygiene, etc. ) and 8 hours to sleep.
Work shifts have an overlap so there is always 2 persons working together as needed.
Security person awareness would be increased with the shorter shift. Instead of maintaining a Status quo there is now time to rebuild.
Add a 7th adult would permit rotating the shifts and provide for illness and injuries.