Huh? I see this sign frequently. So I went ahead and figured it out. The diagram below reveals the door schedule. I assigned a number to each of the times the door is closed, 1=9:30 pm - 4:00 am ; 2 = Monday - Friday; 3= 9:30 pm etc.. So I guess they only unlock the stair wells on weekends when no one is in the office. Must be a security measure. :) Sat, Sun Mon Tues-Thurs Friday Holidays 00:00am-04:00am 1 1,2,5 1,2 1,2,4 1,6 4:01-9:29pm OPEN 2,5 2 2 6 9:30pm 1,3 1,2,3,5 1,2,3 1,2,3 1,3,6 9:31pm-11:59 pm 1 1,2,5 1,2 1,2 1,6