When should I apply for a new extension of my Non-O visa based on marriage?

You need to keep 400k in your bank account for two months to extend your visa for 1 year

The key is entering the country on 420… Shows extra respect for the 300,000 new jobs 🌿🙏 created

I think I seen a prior post where you was moving or in Maha Sarakham. You can do your one year extension based on marraige 45 days in advance. Just did mine one week ago.

You don't need to apply for a new non-O, you need to apply for a one year extension of stay. At the moment your stay permit expires on 18th July. You need to go to immigration and apply for the one year extension when you have no more than 30 days left on the stay permit (so after 18th June). Some immigration offices let you apply earlier, when you have no more than 45 days left.

This is something you need 2 photocopies of every document necessary, signed & hand in in person at your local Immigrations Office.

A yearly chore so long as you still stay in the same legal marriage, but that's how it done unless you use an agency?

Why not get a marriage visa, but I would start about weeks before that should give you enough time to get all your paper work ready

That is not your visa.Assuming u applied in your home country u should have a 1 year visa.Hopefully u applied for multiple entry.When u arrive in Thailand u will get a stamp in your passport as u have shown.The O marriage visa is a one year visa but it requires a departure from Thailand within 90 days exactly as your stamp shows After u departe and re enter u will get another 3 months.U cannot get this extended at immigration it requires physical dept and entry which u can do each 3 months until the 1 year visa expires.Then u need to get a new 1 year visa.

I did it three weeks before the expiration date but I had to go back two more times. Go through an agency.

Assuming you are meaning to apply for the year extension you have to do it on or before 18th July. Suggest doing so a couple of weeks or so early just in case you need extra paperwork or something.