Will I avoid overstay fines if I leave Thailand before my flight on January 28th?

okay first off what's up with cutting it so close that you're counting the hours ?? I mean WTF?

Secondly, If you're flying out, and you have an overstay of under 24 hours you do not get fined the 500 baht AND you do not get the big overstay stamp in your passport. Instead you get a small thai language only "overstay of under 24 hours fine waived" stamp and you get to leave. Like this

no.problem ! they dont do anything for 1 day

Reach airport before 11pm and meet the immigration officer. As you are at airport on 27th and not overstayed. You will have no problem. There will be no fine. No problem at all. Secondly do your online checkin for your flight on 27th itself and print your boarding pass.

The time you walk through immigration isn‘t what counts. You do have to show your boarding pass to the IO and they do see the departure time. Then it is up to them to let you through or referr you to a supervisor.

Minimum pay 500 fine for one day only

The check in counter will open 12:30am so I don’t think you will be able to pass immigration before midnight. Don’t worry, if you pass immigration around 1 or 2am you won’t be paying an overstay fine.