You cannot extend a visa. You can extend your stay on the basis of a visa or on a visa exempt. It depends on the kind of visa you have and on the rules of the Immigration where you apply for it. Every hotel is obliged to issue you with a residence certificate (TM30). When you leave the hotel, your residence ends. If you have the TM 30 certificate, then go to the nearest immigration office. They will tell you whether you are too early or not. You still haven't written where you want to apply for an extension (30 days). I also don't know all the different deadlines of all 64 or more immigration offices in Thailand.
A person whom I am allowed to insult, and who absorbs everything with his seemingly endless tolerance for frustration and who has nevertheless helped me over many years with his meticulous knowledge, I wish for him today that he stays as he is and that what he wishes for himself comes true.🍓🍓