Just back from CW after getting tourist visa exemption extension. Arrived at 6.45am and got entry number 700! By 8am that was almost double! Thankfully counters opened at 7am again, and I was all done by 11.15am.
TLDR : Answer Summary
The post describes a recent experience of extending a tourist visa exemption at a Chiang Mai immigration office, detailing the arrival time, queue number, and total processing time. A comment adds a similar experience with a different arrival time and processing time.