I’ve gone at 0800 and they open at 0900 two times with different wait time. First time I wait about 1.5hrs and second time about 6hr that’s including them closing for lunch at 1200-1300. Both times was to get an 30 days extension. It’s really a hit or miss on how long you wait but going early would be better than afternoon.
Previously, I have had my tm30 filed by owner 3-7 days after I arrived. I forgot how many day but it was for sure after 24hrs of my arrival. Went to apply for an extension a week later and I was fine. However you are supposed to have your tm30 filed within 24hrs of arrival but I feel that in Thailand lots of things are situational and the immigration officer you get. Some are nice and some are not.