@Bob **********
right at most offices you can go when you have 30 days or less left on the current stamp, and you can go the very last day the stamp is good for if you want, although that is NOT advised seeing as if you are short a document, copy, etc you don't have time to sort it out
That's why most people go once they have 30 days or less left on their stamp, there is no down side to applying early the year extension is added to the current expiration date of the 90 day Non-O visa stamp
Just noticed that is from Chiang Mai, and you can apply for the year extension when you have 45 days or less left on your 90 day stamp (once you get it) and in Chiang Mai they issue the extensions on the spot (you don't come back to pick up the passport)