Thailand forum

Bangkok Airport is huge and there are miles of corridors so you need to factor in walking time too. Two and a half hours might just be enough time though.

Immigration queues can be quite slow. It might take 30 minutes for your immigration formalities and maybe an hour for your girlfriend. (Just guessing for the girlfriend, might be less than that). By the time you get through immigration your bags should have arrived though. Not sure when the Bangkok Airline check in counters close but, assuming your incoming flight is on time, that would still give roughly an hour and fifteen minutes to check in and get to the departure gate. This is a bit tight but it is doable as you won't have to go through immigration again.

well customs always take some of your time though, 2,5 hours should definitely do the trick.
I most be arriving always when there's now one at customs, never had to wait longer than 2 minutes.

If you really want to go faster, try to fix a wheelchair somewhere and go trough special customs . not advisable if you don't really have something :p.

Clearly we're talking about immigration here rather than customs, since picking up your bags and walking through the green channel won't take you long. But as others have said, it can vary so much depending on the queues at immigration.

With visa exemption that (the queues at immigration) should be your only concern, but visa-on-arrival will take much longer. I've not done it myself, coming from the UK, but from what I've observed your girlfriend can expect to have to fill out her application and pay the fee before she reaches passport control (I don't believe VOA is covered by the current free tourist visa scheme - anyone know for sure?), get her visa and then finally proceed to passport control with you to get her stamp in.

And as others have said, Suvarnabhumi is a vast maze and getting from an arrival gate at one end of the airport to a departure gate at the other can take an age - my family missed their return flight to the UK last summer for precisely that summer (they actually saw the plane taxiing down the runway as they got to the gate - how irritating!)

I don't suppose you can transfer through the airport to your Bangkok Airways flight, and then complete immigration formalities on Samui, rather than exiting at Bangkok and going back in? I don't know if that's a possibility, perhaps you can only do that if you're doing both flights with the same airline? But potentially something to look into.

If not, you might just make it, but I know from experience than Bangkok Airways are pretty strict on their check-in counter and gate closure times (I also missed a flight to Samui with them last year because of traffic on the way to the airport!) so personally I would feel much safer with the 9am flight.

Good luck deciding, and enjoy your trip!