My first trip was in 2004 and of course used Don Maung at the time. 15 trips later to both DMK and BKK and I never waited more than 1 hour and that 1 hour only happned once. Now, having said that, I have seen a few reports and photos of the immigration queue going down the ramp and pretty far back into the hallway. Sure somethings happen now and then, security alert, shortage of staff, computers down, unusual number of same time arriving flights, etc. I typically arrive around 11 AM from my LAX through Taiepei connection although I have arrived at 2 AM and then.