I had to travel oversees urgently and now will miss doing my first 90 day report in person! But I remember a while back Tod saying that coming through the airport immigration resets this...can anyone confirm this for me?
TLDR : Answer Summary
The 90-day reporting period for foreigners in Thailand resets upon entering the country, meaning that your 90 days start from the date you cross the border into Thailand. If you have to travel overseas and miss your reporting deadline, entering back into Thailand will grant you a new 90-day period.