Not quite true. The number of days is dependent on office. Some like Bangkok, Chiang Mai, Phuket, etc allow 45 days prior. Most allow 30. Some like Jomtien, Samui and Koh Phangan only allow 7 days prior.
Some offices require you to fill STM2 and STM9 as well. They’re not difficult to do and will be on hand at the office if needed.
That’s for the initial Non O visa. That needs those number of days to convert. You can extend an extension up to the actual due date but actually 5th for you.