I had to fly home to the UK with Thai airways during covid and I flew to Suvarnabhumi from Udon with Thai Smile to get the flight. I had much more legroom on the domestic flight then I had flying from Thailand to the UK. Nothing is logical in Thailand...555.
THERE IS NO CHARGE FOR A ONE DAY OVERSTAY AND IT HAS NOT BEEN CONSIDERED SERIOUS IN ANY WAY. I HAVE HAD AN IO AT THE AIRPORT MAKE LIGHT OF IT SAYING WITH A SMILE SOMETHING LIKE WHAT A NAUGHTY BOY YOU ARE. I HAVE DONE IT AT LEAST THREE TIMES OVER THE LAST 17 YEARS WITHOUT ANY REPERCUSSIONS SINCE APPLYING FOR OR EXTENDING VISAS.
I'm speaking from experience over 17 years. I've done it at least three times entering by land and air many times since with various visas and had no problems. Also the arseholes at my local immigration office thumb through my nearly full passport over and over again trying to find something to find fault with but they never can because I am totally legit.