I am impllying that everyone that could get in BEFORE the zombies have arived is already within the safe area on the other side of the fence.
you do NOT open it for 4 humans being chased by zombies just because they might make it before the zombies catch up to them because most of the time it will backfire and get the rest of the team tagged.
the same way you do not open a cade for the 2 or 3 unlucky people wandering around looking for a cading spot after the zombie has spawned and tagged a few people
Edit: Valve AND Zero would find a way to screw up a steel ball.
I have never seen any other server that used to be so much fun to play on just get so properly rammed into the ground by one person's lazyness, incompetence and inability to grasp how to properly run a server.