Is two days enough to renew my retirement visa in Chiang Mai before it expires?

The big issue will be getting everything from the bank. If you use Bangkok Bank it takes 5 working days to get the 12 month statement you will need, others may issue there and then. I'd suggest the bank should be your first stop and then immigration

In Chiang Mai you can apply for a new extension when you have 45 days or less left on your current stamp <meaning from 45 days before right on down to the day your current stamp expires

Obviously the closer to the expiration date you apply the less chance you have to correct any issues (missing documents, etc) that come up in the application process. 😮

𝗜𝘀 𝘁𝘄𝗼 𝗱𝗮𝘆𝘀 (𝗧𝗵𝘂𝗿𝘀𝗱𝗮𝘆 𝟭𝟵𝘁𝗵, 𝗮𝗻𝗱 𝗙𝗿𝗶𝗱𝗮𝘆 𝟮𝟬𝘁𝗵) 𝗹𝗼𝗻𝗴 𝗲𝗻𝗼𝘂𝗴𝗵 𝘁𝗼 𝗿𝗲𝗻𝗲𝘄 𝘁𝗵𝗲 𝘃𝗶𝘀𝗮?

As I said you can apply right up until the date your stamp expires (and if it expires on a weekend or a day the immigration office is closed but you go the very next day they're open you can even apply then too without getting an overstay fine) 🙂

𝗜 𝘄𝗼𝗿𝗿𝘆 𝗮𝗯𝗼𝘂𝘁 𝗵𝗶𝗰𝗰𝘂𝗽𝘀/𝗽𝗿𝗼𝗰𝗲𝘀𝘀𝗶𝗻𝗴 𝗱𝗲𝗹𝗮𝘆𝘀.

The worry is you don't have every document, copy, bank statement, bank letter, updated bank book, TM30, lease, etc that you need and you run yourself out of time 😕 So that burden is on you to get it right in the time you have left 🙂

𝗜𝘀 𝗶𝘁 𝗼𝗸 𝗶𝗳 𝗮𝗽𝗽𝗹𝘆 𝗯𝗲𝗳𝗼𝗿𝗲 𝘃𝗶𝘀𝗮 𝗲𝘅𝗽𝗶𝗿𝗮𝘁𝗶𝗼𝗻, 𝗮𝗻𝗱 𝗿𝗲𝗰𝗲𝗶𝘃𝗲 𝘁𝗵𝗲 𝘃𝗶𝘀𝗮 𝗲𝘅𝘁𝗲𝗻𝘀𝗶𝗼𝗻 𝗮𝗳𝘁𝗲𝗿 𝗲𝘅𝗽𝗶𝗿𝗮𝘁𝗶𝗼𝗻?

That wouldn't happen. C/M doesn't have you come back and get the passport on another day.

You would apply before the stamp expires and they issue that extension the same day.