If your nationality is eligible for visa-exempt, yes, you will be stamped in for 30 days on it and 30 days tourism extension is applicable.
I would contact LTR BOI in advance to jump in that route to make sure there wouldn't be any issue for LTR processing in your case if the current status is changed (on retirement extension -> visa-exempt).
Better check if 5. note 3 or similar thing is applicable to your case.
Check your local immigration office. You may need to get some documents from your employer along with your work permit, such as company letter (and contract), tax documents (forms and proof of payment), company certification, photos from work, etc, etc.
You don't have 23 hours to leave. That is wrong information or they might have wanted to say 23 o'clock. You have until 23:59 that day of cancellation to leave Thailand when you apply for cancellation and do nothing. If you need longer, you do as Tod says.
Your 90-day counting will stop when you leave Thailand and start again on the arrival date as day 1.
90-day reporting system automatically generates a notification email from your last report online. It is not linked to your entry history.
When you travel out from and back to Thailand, you need to count your new 90-day report due on your own.
And remember, you travelled abroad since the last 90-day report, next 90-day report in July has to be done at the immigration office in person as it is the first report after re-entering Thailand.