Air Asia - tight connection possible
 

I am flying from Siem Reap to Don Mueang to Chiang Rai on Air Asia with two separate tickets (I haven't bought the 2nd ticket yet). The 1st one lands at DMK at 12:50 and the 2nd one departs at 13:55. Is 1 hour enough time to get through immigration and make my 2nd flight? I will only have a carry on bag, no checked bags.

Probably not. Buy a later ticket.

Thai Smile will sell you a connecting ticket.

Is there not a fly thru price with AirAsia for this journey? If you can book flythru then a member of AirAsia staff will meet you at DMK as you exit the aircraft and escort you through the transit process. You cannot self transit with AirAsia at DMK and with the connection time you have suggested you would almost certain to fail to make your connection by going airside.

It seems AirAsia's only flythrough option when taking FD 611 (11:45 from Siem Riep) is a flight from DMK at 20:20 arriving at Chiang Rai at 21:45. Wait time of 7 hours 30 minutes at DMK. I assume that's how come the Op's looking at booking separate tickets. Doing that, the only available flight from DMK to Chiang rai (before 20:20) is the 13:55 (FD 3207) arriving in Chiang rai at 15:20.

Presumably the OP needs to arrive in Chiang rai earlier than 21:45, hence, the fly-through options are a no go....Or, the OP feels the wait time of 7 hours 30miutes in DMK is too long.

Looks like Nok air has a daily flight at 17:00 from DMK arriving at CEI at 18:25. Not sure if their timeliness record is comparable to Airasia's. But the cost seems lower and it will shave 3 hours off the journey (compared to booking the 20:20 from DMK with AirAsia).

Thanks everybody for your input. knav2013 is correct. Even worse than the 7:30 hour layover is the flight would cost me more than twice as much as booking the legs separately. I think I am going to go ahead and book the 1700 flight with Nok Air. I can live with a 4 hour wait since part of that time will be wasted going through customs anyway.

if everything goes well: flight on time and dock at the terminal, you sit towards the front of the plane and immigration is fast (or you can use the priority line), I guess it is feasible as you don't have check in luggage. Otherwise it seems really tight

If you are prepared to buy new ticket to CNX if you miss your FD flight to CNX (mind you, domestic flights in Thailand are fairly cheap even last minute, so not the end of the world) then by all means take the chance and go for the earlier flight - without luggage there is a fair chance that you will make it. There is nothing more annoying than booking the later Nok Air flight and then on the day of traveling realising that you could have made the earlier (and possibly cheaper) FD flight.

The FD flight is definitely not cheaper (I've checked).

I suppose one could check a website like flightradar24 and see how punctual FD611 has been in the past, then make an informed decision. However, with this schedule you really have to hope for FD611 to land on time or earlier than usual, because as fas as I'm aware boarding gates close 20 minutes before departure. So, if FD611 lands at exactly 13:00 it will give you 35 minutes to get to the boarding gate for FD 3207. Actually, it'll be much less time than this, because after the aircraft lands, it usually take 5-10 minutes to taxi. Then depending on whereabouts you are sitting it may take a while to exit the aircraft. All these needs to be factored in.