Your walls hold the line, your supplies await your return, and the timer never takes a day off. A base with a flag has a countdown of five real days before removal. Simply logging into the server does not extend it.
How to keep your shelter
Approach your base flag and use the Refresh action. A new period of five real days starts from that moment. The time remaining appears in the flag action label: it is the current remaining time and decreases as time passes.
If you leave it too late
When the timer expires, the system automatically removes the flag and nearby Building System structures, including walls, fortifications and other structures belonging to that system. You will have to rebuild your shelter. This does not mean that every object on the server is removed.
Before your next expedition
Check your supplies, equipment and base timer. Refresh the flag early, while you are still standing next to it. Merak has enough unpleasant surprises without returning to the spot where your wall used to be.
Supplies packed. Equipment checked. Flag refreshed.