After paying an overstay, how long before you can return

My son (an American citizen) went to Laosand got a tourist visa 3 months ago. When he came back to Bangkok he said: Hey, they gave me 3 months instead of two, this must be something new! (Unfortunately, he was looking at the expiration date of the visa, not the entry stamp.) When the 3 months were up, a couple of days ago, he went to Chaeng Watthana to try to get a 30-day extension. They informed him he had a thirty-two-day overstay and he must go to the airport the next day, pay a fine & leave the country. He asked the immigration lady if he could fly back to Laos and get another Touristvisa. She said that would be OK.
He flew to Laos the next day and went to the consulate to apply for the tourist visa, but when he got there, there was a sign on the door saying they were no longer taking drop-ins for visa applications, everyone must make an online appointment before they will be admitted inside the consulate, so he went back to his hotel to make an apt. But the appointment program said the first available slot was in twenty-nine days! He decided to fly back to BKK the next day, and get a 30-day transit pass, then go to Penang to get the tourist visa before the 30 days were up.
So, today, he flew into BKK, & waited in the immigration line. The officer said because of the overstay, he would not be allowed to enter the kingdom without a ticket out, so he got out of line, and went and bought a ticket to Hong Kong, stood in line again, and this time the agent he would not be allowed entry even with the outbound ticket. The agent called Laos air and said they would have to pay a fine for allowing my son to come to Thailand without an outbound ticket. The Laos Air official forced my son to buy an expensive ticket (back to Vientiane) for tomorrow morning, they then locked him up over-night in a detentioncenter, where he is right now. (He also has to pay 1000 Baht for detention-center rent.)
He asked Thai Immigration how long he is barred from enteringThailand. The officer said: Im not yourteacher, it is your responsibility to know the law.Ive spent the last hour searching the internet for this law and I cant find anything.
Does anyone know the answer, or at least where I should be looking?