When to report 90 days?

The notification is mandatory for every tourist and Non-immigrant who stays in Thailand for 90 days or longer.
That's the starting point.

Immigration allows you to do this from 15 days before to 7 days after the 90th day.
However, this does not mean that if you leave on the 93rd day, you will be released from the reporting obligation.
You have been in Thailand for more than 90 days and so you must make that report.

He will normally be able to leave without any problems. Immigration will not say anything about this at passport control.

However, when he returns and he makes a 90-day report next time, there is a chance that he will still be contacted about it. This normally remains open during immigration.
It then depends on the immigration officer whether that previous report is closed without any follow-up, or whether he will still be fined.

Dear Edward,
The best advice you can give go for Feb 15th. for your 90 days and don't forget your re-entry.
That way you have the least misery.
Greetings and success.

You don't even have to go through Immigration. You can handle everything by post, but you have to make sure that your application is at Immigration 15 days before the expiration date. The list of necessary papers (including prepaid and addressed return envelope) can be found on the Immigration website.