FYI - American entered on visa exemption. I extended today at IT square in Bangkok - although you can do it online now there is practically no wait. Arrived at 8:40 and out in less than an hour! I made sure my tm30 was completed, 1900 baht (I always bring exact change), photo and photocopies of passport can all be done there.
TLDR : Answer Summary
An American expat shared their experience extending their visa exemption at the IT Square immigration office in Bangkok. They noted that, although online extensions are available, the in-person wait time was minimal, taking less than an hour. They arrived at 8:40 AM and found completing the TM30 form straightforward. The total fee for the extension was 1900 baht, and they advised bringing exact change as well as a passport photo and photocopies, which can also be prepared on-site.