When should I apply for a 60-day extension on my O visa?

If you have an actual type O visa that expires in January, then why do you not do everything needed to extend it for a full year, as you should be able to do that, if you can meet the financial requirement for a dependent, as long as the child lives with you, even if you are not married to the mother.

Now immigration give 60 days extention every time you visit for Non immigrant visa ?

IF you are wanting to stay as long as possible, I'd say apply for the 60 day "unable to travel due to covid" extension next month (because those extensions can't be applied for after Jan 29th) AND hold back on the 60 day visit thai family extension (because you can only get that one time per entry) and if you get it when the 60 day covid extension would be running out (in 2 more months) you'd get to stay longer.

Are you talking about applying for the 60 day unable to travel due to covid extension? NO matter what reason you're wanting the 60 days you should wait until closer to your current entry stamp expiration date before you apply for it.

There's no need to run to the immigration office now to apply.

Also remember it's not the expiration date on the VISA that matters at all. It's the expiration date on the red entry stamp you got from the visa that matters :P :)

You can only get a 60 day extension based on visiting thai family if you're married to a thai OR have a half thai child.

As far as I am aware you can extend a month prior and not lose any days as long as you meet the criteria for the extension