Can I apply for an early extension of my non-O visa in Thailand?

Can extend 45 days from the date of visa expire.

Do you have Thai family (wife or child)? If you wanted to change when your next extension application is due to might be able to get the 60 day Visit Thai Family extension (requires a Thai wife or child) if you have not yet taken this extension to your initial Non-O visa? This means your next 12 month extension moves out those 60 days.

I was in your situation as mine was ended on the 18 May and had to travel to renew on the same day and the funny think is the immigration at Suvanakhum did stamp my passport for only 1 day.

why are you running your stamp down so close to the expiration date before you apply for an extension?

At most offices you can apply for an extension when you have 30 days or less left on your current stamp.

Bangkok, Chiang Mai, Phuket and I believe Pattaya you can apply for an extension when you have 45 days or less left on your current stamp

There's no reason to wait until your current stamp is almost running out because the extension is ADDED to the expiration date you have now no matter when you apply (within the window the immigration office you use allows) meaning you don't lose any time applying early :)

You have to see how early your office allows you to apply for an extension AND

if you're still not going to be in country when it's the soonest you can apply you need to ask them if you can get an early extension with proof you're not going to be here during the regular renewal period (although the immigration office doesn't have to let you, they can allow you to do it but it's their call).

You might have to just get a new Non-O visa when you're out of the country and start the process for the extension again, once you get back.