When can I apply for the one-year extension of my Non-O visa in Chiang Mai?

Hello, I received a 90 day non-O visa based on marriage to a Thai which expires on November 18. When is the earliest date that I can return to the Chiang Mai immigration office to request my first one year extension? When I picked up the visa, the immigration officer told me to return on Nov 18th to apply for the extension, but that seems like a risky proposition to me. I have seen posts suggesting that one could apply as early as 30 or 45 days before expiry. Which would work and on what basis is this calculated - calendar days or business days, recognizing two holidays in October? Assuming the latter and 30 days, would I be able to apply from October 5?

Thank you for your advice on this.