What are the rules for 90-day reporting in person at Bangkok CW, and can I renew my retirement extension on the same day?

As Tod says .. no problem with your dates . Last month i had it the other way round . Renewed my visa extension and tried to do a 90 day but they told me ( very politely ) to come back within the 14 day or 7 day windows .

For in person reporting you can do it from 2 weeks before the due date down until 7 days after the due date without a fine <- so you have a 3 week window to file

No issue at all doing your 90 day report the same day you do your retirement extension.

Just realize the 90 day reporting room at the government complex Building B moved from the main immigration room on the 2nd floor (where you'll apply for your retirement extension) to it's own room on the 3rd floor.