Hi, I'm doing a visa run from Chiang Mai to Savannakhet and I need help with the buses. I arrive at Udon Thani Airport at 5:10PM, Monday the 25th and need to catch a bus that evening to Mukdahan so that I can cross the border the next morning. Where do I go to catch the bus. Oh, details--is there even a bus that goes all the way that late?

There are 3 places in Udon you can be let off a bus. Most likely you will land at Bus Station 2 (Northern Bus Station) (On the outskirts of town on the road in from Loei towards Nong Khai). Buses to and from northern Thailand such as Chiang Mai, Chiang Rai. A tuk-tuk into town costs about 100 baht from there (Dec 2014). Songthaew 7 will take you there as well. Check there for buses to Mukdahan.

There is also a downtown bus station. Worst case, you may have to take a tuk-tuk there. (There is a third stop, Central Plaza, that only Phetprasert buses stop at. [Always useful to indicate what bus company you are on]).

I would be very surprised if you could not get a bus to Mukdahan later than 17:10. It's only about 4 hr away.

If you could you would be better off to fly to KK and then get the KK Mukdahan bus, that goes about every 40 minutes to at least 6PM, maybe later. There is also a minibus from KK, but I don't know when it runs.