When should I apply for my Non Immigrant O-A visa renewal before it expires in Thailand?

Correct. When you enter on a valid OA multi-entry visa you get stamped in for a calendar year OR as long as your mandatory 100K USD health insurance is valid for (up to a year)

So as long as you enter before the visa itself expires (which you says is Oct 24th, 2024) you'll get stamped in until your current mandatory insurance expires (which you say is June 30th 2025). (y)

You don't renew visas, they run out when they run out. and your VISA is gonna run out on Oct 24th 2024. BUT your "entry stamp" <- which is what lets you stay IN thailand is valid until the 30th of June 2025.

You would apply for a yearly extension at the immigration office when you have 30 days or less left on that entry stamp (or around the end of May next year)