Thanks everyone for your advice. I just got through on the Immigration hotline phone number, they said you do need to leave the same day as cancelation for a Non O-A. He's changing his flight to late-night to do it on the same day.
He did, they told him to cancel OA at immigration. My question is after canceling the OA, how long does he have to leave Thailand? I mean even a day or two, or does he have to leave that same day?