How many days in advance should I report to immigration to extend my Non-O marriage visa in Thailand?

Can do 45 days before visa expired, better do now.

It depends on your immigration office. Some like Bangkok, Chiang Mai and Phuket (and some others) allow up to 45 days prior. The rest are usually 30 days prior. There is no minimum period. You could apply the day your visa expires - but highly not recommended to do that. Get it done as early as possible for your office. That way if there’s any issues with paperwork or requirements you have time to sort it out. They add a year on to your existing “allowed to stay” date so there’s no downside to applying early.

You must go at least 30 days before it expires, but no more than 45 days.

Now

For visa you can go 45 days prior to expire date