Can I apply for my non O visa extension 40 days early without losing time?

No you will not loose those days

In Hua Hin you can do it 45 days earlier snd you not loose 1 day. Make also the re-entry if you plan to leave the country once.

At most offices you can apply for an extension when you have 30 days or less left on your current stamp, SOME offices like Bangkok, Samut Prakan, Chiang Mai, Phuket etc allow you to apply when you have 45 days or less left on your stamp.

Unless you're changing the reason for your extension (like marriage to retirement or retirement to marriage) all extensions are added to the expiration date you have now. <-Meaning you don't lose any time applying early.