I just wanna share experience. I just got back from Muangthong Thani Immigration Office to extend my visa exemption, it takes 30mins from giving all documents to officer until get my passport back. Approved with 30 days extended , when arrived at airport they stamp 13 Feb as exit date limit, now its 15 March 👍👍
Note : on the ground floor there are photocopy booth to copy all documents needed for visa extended. For extend visa exemption we have to go on 3rd floor, and then first step there is one counter for checking our passport to check which visa we have, then the officer will give the form to fill in. After fill in the form we bring it back to the counter so the officer will check all documents, copy of passport ( front page with our details & page with stamp from immigration at airport and copy TM6 departure card) and 1 photos (4cm X 6cm). After officer check all required document completed, we have to sign all documents and then put our phone number below the photograph. And then we go to second counter to bring all documents and they will take photos and we pay 1900 THB. After that we just need to wait form them to call us if passport with extended visa is ready. Thats all the steps in my experience, i dont know if somebody else have different experience.