The number is based on the amount of tasks requiring attention. If your flights are clustered together and a big crowd of passengers passes through your terminal, there will always be a lot more tasks than individual janitor. But over the next 1-2 game hours you’ll see the tasks reduce back down to near zero mine peaks at about 500+ jobs requiring attention, but after the last flights of day have left, you see the janitors slowly reduce that queue down to only a few jobs