I recently got a 30 day extension stamped in my passport untill the 30th October, my outbound flight leaves 0.15 31st October, so i will go through immigration @ BKK approx 21.00 on the 30th, but technically i don't leave till the 31st, i forgot to ask at immigration in Nakhon Ratchasima if this would be aproblem, in my excitment at obtaining my extension, So would seem extreemly harsh if they do me for 1 day overstay, So any input would be welcome! tia

 

A one day overstay is really nothing to worry about.

You will not be fined 500 baht for a one day overstay when leaving the country at the airport.

You will get departed stamp in your passport when you pass immigration at the airport. If you pass before midnight you will not have an overstay.

Nothing to worry about here. Even if you miss the flight or it is cancelled, a 1 day overstay is not even assessed the B500 fine. More than 1 day overstay and it's B500/day including Day 1, if memory serves. 

10 minutes ago, Skeptic7 said:

More than 1 day overstay and it's B500/day including Day 1, if memory serves

Correct

I did exactly this on our last trip (on a TR60) here, Thai Airways changed their timetable mid trip and moved us to a 16 hour BKK>HKT>LHR flight on day 58, after asking nicely they moved us to a direct flight on the 61st day @00.15 Hrs. Not a problem as we obviously cleared immigration earlier in the evening of the 60th day. Certainly maxed out the value of the TR60 Visa!