Can I get my 1-year Retirement visa the same day I apply in Chiang Mai?

Issued day you apply if all in order.

You won’t be doing it on Jan 6 it’s a Saturday

If you are meaning you’re applying for the initial Non O visa off a tourist or exempt stamp then there generally is an under consideration period as that office may not have the “authority” to sign off on such a visa and has to send to their HQ to process.

If you already have that and are actually going for your one year extension off of the Non O then usually you’ll get it same day or next day (so the head of the office can sign off on it).

I assume you already have the 90 day Non-O retirement visa and this will be your first 12 months extension? If so they are normally issued on the day you apply.