Roughly how long is the waiting time to get a 30 day extention of stay for a tourist visa at Chaeng Wattana if you go after lunch? Is it a lot quicker than an ED visa where you spend half a day to 3/4 of a day there?

Go at the right time and it can take 30 mins. I have found later in the afternoon to be best. Also Tue-Thu are the best days. Can vary a little though.

I did a 30 day extension for a tourist visa in August.

Arrived at 9:30 A.M. with whole thing finished and done before 11:15 A.M. including making photos and copies downstairs on first floor.

Even had time for a cup of so-called non-fat Gelato (Black Forest flavor) at the Gelato shop downstairs before I caught a taxi back to where I live in Bangkok

Was a Friday as I recall.

Not a very busy day.