Can I file for a non-O (marriage) visa extension on the last day of my visa in Chiang Mai?

I once did mine the day after due because the day due was a Sunday (January 2nd.). The only problem I had was with the bank which was refusing to do the statement of balance because it was after the due date. My Immigration Officer was furious with them for creating problems which were none of their business and made a very stern phone call to the bank branch !

Last time in Bangkok I had 14 days left, it wasn't mentioned, seems no problem at all.

Immigration offices have air con so shouldn’t be hot

Never leave it until the last day what happens if they request more documents and everyone gets an under consideration stamp

Like Tod says don't leave it till your last day if anything is not right and you have to go somewhere to fix it your putting pressure on yourself to get it done that day and if sick that seems like putting pressure on yourself for no reason. Good luck

They are correct, in Chiang Mai you can file for an extension of stay when you have 45 days or less left on your current stamp <- that means from 45 days before your expiration date right on down to the last day the stamp is valid for.

We DO NOT recommend that you burn your stamp down to the last day because if you are missing a document, need to "fall back, re-group and try again another day" you're running on overstay

You have no choice on the under consideration time it's 30 days ADDED to the expiration of your current stamp, so apply 45 days early you wait 75 days (45+30), apply the day your stamp expires you wait 30..