Hey I am trying to book a ticket leaving Chiang Mai on the 21st, and returning on the 21st. I do not want to stay the night in another country. I've tried ThaiAir and AirAsia:

Thai Air

Chiang Mai (CNX) -> Kunming, China (KMG) 11:30 -> 14:05

Kunming, China (KMG) -> Chiang Mai (CNX) 15:20->16:00

Layover is 1hr 15m

AirAsia

Chiang Mai (CNX) -> Kuala Lumpur (KUL) 9:10 -> 13:00

Kuala Lumpur (KUL) -> Chiang Mai (CNX) 14:45 -> 16:25

Layover is 1hr 45m

Are these layovers too short/low chance to catch? I can book both tickets one way, but I'm not sure if the airline will let me fly once I get to the airport? I do not want to stay the night in another city/country. Any advise? Thanks in advance.

So the OP I might presume is planning on following the signs to TRANSIT once landing in another country and not going through the formal entry/exit process in the country ex-Thailand. OK.

the THAI AIR flight on which you want to return to Thailand is basically on the same aircraft that you used on your way out. I believe this is 100% impossible as you WILL have to go through Chinese immigration (do you have a Chinese Visa?) and I am very sure they smell a rat (even if there actually isn't one) if you IMMEDIATELY want to leave again - it is a hassle to get a China Visa after all, so why would someone immediately leave again, they will think.

The KL itinerary COULD be doable if there is no flight delay, but again you WILL need to go through Malaysia immigration twice. very risky

KUL could work.

Or you invest a few extra Baht and use a return flight from KUL via DMK to CNX.

KUL 15:35 - DMK 16:50

DML 18:10 - CNX 19:20

Kunming? Never.

Will you apply for a China visa (or is it visa exempt for you)?

Forget China.

If you are a risk taker, the Air Asia option via KL is more likely than not to work. Fortunately, the outbound journey is a morning flight which means (even on Air Asia) that there is a fair chance it will not be subject to a long delay. Worst case, you may be faced with buying a new ticket via Bangkok.

Is it just by chance that another old thread about CNX to KUL has been revived (other poster).

Have you noticed that AirAsia will not allow a return booking for this?

Your return flight should not be earlier than your departure flight. Please select a later return date or time.

The message is not quite correct (generic) but indeed they will not accept this as a return flight.

I do not know the official policy stating that one must, upon exiting Thailand, legitimately enter another country before returning to Thailand. I first encountered this at the Friendship Bridge at Nong Khai where it was possible to exit Thailand, take the shuttle bus across the bridge, and then step over a small barrier to return on the shuttle bus without ever entering / exiting Laos. All such persons were denied entry into Thailand and sent back across the bridge to Laos.

One has to go through immigration in the other country, as people said already. One cannot stay in transit and tae the next plane. Thai immigration wants a stamp from the country one comes from.

That beeing said, i usually did this "border-flight" with 2 seperate airlines via KL. Fly there with Thailionair and fly back with Air Asia. But its really tricky, you have not much time. If the arriving plane is late then you could get problems.

Last time i did this (in January this year) i had around 1 hour to checkout, check back in and all that. But there was so many people on the counter that i had to ask if they let me checkin before them. Otherwise i would have missed the plane.

So, its possible but you have to take seperate airlines probably.

Well I don;t know why everyone doing this seems to want have the absolute minimal time between flights and to enter/exit whatever country even if like HKG the passport is not ink-stamped but I guess that I just do not have the same busy schedule as some on here.