went to chiang mai immigration for 90days . drive thru, took only 30s. just with passport and old slip. really really. not kidding. just 30s and out again. no forms to fill too. amazing
TLDR : Answer Summary
A user shared their experience at the Chiang Mai immigration office for a 90-day visa extension, reporting that the process took only 30 seconds with no forms to fill out, requiring only their passport and an old slip.