As an experiment and to compare with CW I found the online appointment site for Chiang Mai, and it has IMO clearer options for appointment selection, and also doesn't require email validation as a preliminary step. So I selected "Retirement Purpose" to find a date.
March is fully booked so I checked April, but it also had no available dates. Despite being greyed out I tried clicking on a day to confirm that's correct, and it displayed "There is no availability on this date" so that's in fact how it works.
So I clicked forward to May...no dates. Finally June, and it has one day the entire month available. Beyond June, you may not pass.
One day, in the next three months. So with 30 days and even a 30-day extension you'd be out of luck. I think there was a recent marriage visa thread about the appointment system, so online appointments and CM may not mix.
Has anybody here done the initial Non-O there recently? Are they reasonable with walk-ins, or is it an all-day or even "All full today, come back tomorrow" affair?