if approved, your 90 days starts from date of the application. Yes you would lose many days. Also if approved, they will keep your application for 15-16 days,then you have to come for the second time to actually get the non/o stamp on your passport.
Same day procedure, available thru an agent I guess. ( In BKK office)
If you plan to extend your non/o based on retirement, or changing from your 60 day tourist/ 30 day visa exempt to a non/o for future retirement extention , then yes. Your bank teller can do all 3 letters at the same time, at the same counter. Easy.
Bangkok bank can issue 3 letters. One is called a credit advice, all in English with sender name, ordering institution and address in your country, other letter will be in Thai verifying money recieved from aboard. The last letter stating your latest 800K balance.
Go where your lastest extension was issued/ renewed/ stamped. IO has to verify in handwriting whose signature it was under the original stamp. So only that office knows who signed.
Request a wheel chair from the check in counter. Tell them your legs hurt. You will get wheelchairs and the services at all stop. You just tip a 100 B to the Thai helper. He will proceed you thru the fast lane.
Unlike tourist visa in Europe, you can enter Thailand on the last day of your visa (stamps, stickers, or evisa print outs) and still get another 60 days from the date you enter. Tourist visa in Europe starts and ends on the date shown in the visa itself.