if it is not approved by Thursday give them a call to remind them. I have had to do this with Kalasin Immigration a couple of times. They will look on their computer see they missed it and get back to you that day with approval. If not you can go in person on Friday.
I have been using the Canadian Affidavit for 15 years now. Have copies of your T4 slips to show them proof of income. The letter they give you is good for 6 months. The fee is $50 Canadian.
I did mine last week in Kalasin, everything went great, out in a little over an hour with a year long extension due to retirement. They even updated my 90 day report for another 90 days, it wasn't due or another month.
I am Canadian and get a letter from the Canadian Embassy, in the 12 plus years I have been doing this, I have not been asked to see a Thai Bank Book. I always take one with me, but do not submit it with my application and have never been asked for it.
If you have ฿800,000 in a Thai Bank Account or can show an income of at least ฿65,000 a month. The Canadian embassy will issue income letters, the easiest way is to come on Non-O based on retirement.
my experience is they will extend your stay to the date of expirey of your passport up to one year. I had an extension of stay from July 29 to January 18 when my passport expired. So 17 months is more than enough time.