Yup, nearly all my arrivals into BKK are after 9:30pm or before 7:00am and I've never, at least since BKK opened in 2006, had to wait more than 15 minutes ... though I fly business and most often I'm the first one or two in line ... I've amassed a collection of nearly two dozen fast track cards because the first immigration area is usually sufficient to fly through.
The one time in recent memory that I had to wait 30 minutes or so was a mid-afternoon arrival on a Saturday.
I also enjoy the brisk walk from gate to immigration ... helps to wake me up and get energized for the ST that awaits me in about an hour.
DMK, on the other hand, was a completely different story prior to 2006.