I heard you can’t apply for the extension until you’re 60 days is almost up and to apply in person. Some people have been told it’s to early to apply even when they’ve been in Thailand for a month.
60+30 each trip. If you’ve been there already 12 days, it’s 60-12 plus the 30 day extension. If you’ve been there only for 12 days then left and come back, you get a new 60+30
Maybe the visa is for one time entry only like most countries. Thailand may not offer multiple entry only student visas. Not sure about other visas. That’s just what I’m thinking.