Did it last week at the new office at One Bangkok. Office opens at 8.30, I was there at 7.45. About 50 people were already there. Elevators open at 8 am (to the 6th floor).
Have your documents ready to be checked at the Information Desk at the very end of the waiting room then you get a number. I was number 18 for re-entry permits. Officers arrive at 9 am. My number was up at 10.30 AM. Recheck the stamp before leaving.