I spend a lot of time in Thailand and I have done border runs travelling as a tourist visa but if I flew out of the country, am I allowed to come back the same day or do I have to stay for 24 hours before I come back?
TLDR : Answer Summary
You can typically fly back to Thailand on the same day after a short trip outside, but re-entry is at the discretion of the immigration officer. While there is no strict rule requiring a 24-hour stay outside, having a clear intent to return, proof of onward travel, and a valid visa or visa exemption increases your chances of smooth re-entry. Frequent border runs may raise questions, so be prepared to demonstrate your travel plans.