Sat. & Sun. open ground floor reception only (not open upstairs, upstairs open Mon-Fri). Must have your correct address (in Thai is helpful to them) - mornings and early a'noons.
I went to Saigon (HCMC).and done, as is the usual case, in 2 days. Just be sure to have crisp, new, not creased or uncut (no cuts at the top/bottom/sides) US dollars both for the Thai Consulate. They will not budge on this issue (my experience).
No need to book an appointment in advance for Saigon (unlike Vientiane now).
You must ask the HR to get the visa cancellation stamp into your passport and hand in your work permit to them ahead of time. Failing that, if they do not have your passport to get the stamp at Immigration, they can receive a letter from Immi (you must a hard copy to take with you). saying that your contract (or most likely) visa has been cancelled.
Either way, you need on of these to happen and then GO STRAIGHT to Mae Sai border - same day if possible, no delay, so book your Green Bus ticket in advance the day you know you will be going.
Hand in your passport (returned to you from HR) and all will go smoothly. The Immi officer will type into her computer the details and stamp your passport.
Proceed over into Myanmar, speak nicely and politely to the military/Immi guy, fill in visa application, hand over the money (check online how much - pay in baht for sure/ US dollars - I'm not sure) for VISA entry, then get stamp for VISA exit.
Hand back into Thailand for a visa waiver for 30 days.
It can all be done in less than one day, but you wish to stay overnight in a hotel if you can't get a Green Bus back to your destination.
Appointment just booked for 28th Dec. One can phone the consulate directly in Liverpool. They were able to advise me of closing times. Always closed on Weds, and of course, they're not working on 25th & 26th Dec.