How soon can I apply to renew my Non-O or retirement visa in Hua Hin?

You can extend up to 45 days at Hua Hin.

You’ll see different answers because each office sets their own rules. Most allow 30 days prior, some allow 45 days prior. I do not know the specific rule for HH but I’ve not seen it on a list of the 45 day ones so I suspect it’s 30 days. I’ll let others with specific knowledge of that office to confirm.