If your going Phuket it’s to the left of the marble steps room 101 I queued in two wrong queues as I approach the office from the side and didn’t see the big sign saying tourist visas
I extended last week at Phuket they were really strict they even went on Google maps to check out my hotel, my advice based on my experience only !! Take your TM30 a picture the correct form filled in for the extension your 1,900 bhart and be confident if they ask about your hotel stay say your not that happy with the accomodation so you are moving in next couple of days I doubt it will be an issue but you’d better go in the morning to allow a bit of time to address any challenges
just don’t tell them your leaving anytime soon as the advice you need to be in the country you applied from less hassle and as it’s digital you’ll get it in your inbox