@Klint *****
i have seen them do it about 3 weeks before the termination of study date on the school's paperwork, but that's the earliest I have ever seen and they had to PUSH hard to get immigrations to do it that early.
Your other option would be to cancel the extension then exit/re-enter the country to get on a 45 day visa exempt entry and use that time to tour thailand ๐ although doing that after comin' off an ED visa (even a valid one) has it's own perils ๐ฎ