I can confirm I entered around 3 years ago on a SETV and extended; After 60 days I converted in-country at Kanchanaburi for a 90 day non imm O based on being over 50, which I then extended for a year, and continue to do so. This was advice from Todd and turned out to be the best option for me..
I have a 160 km drive to my office which means I have to go to my local branch for the docs then do the 3 hr drive. If I thought a branch near the imm office would give me I’d chance it but if they refused I’d have to go back again the next day. Not worth the risk.
you were 100% correct the 90 day date calculation by the IO was 2 days out. I now have an online 'pending' 90 day status which will no doubt stay pending till after the holiday. Thanks again. Have a dry Songkran.