My experience is all at Chiang Wattana, so your mileage may vary, but: 1. I have submitted 30 days before my current extension expired with no problems. 2. I always get a stamp to return in 28 days (exactly 4 weeks) later and I return on that day. Always got my extension on that day. (Many people say 30 days, but it was always 28 for me.) 3. On one occasion, I left Thailand during the 28 day period, but was careful to be back on the 28th day. Be sure to get a re-entry permit AFTER you apply or you will start all over again! Good luck!