I really don’t wanna linger around til 5pm or whatever waiting for a bus, is there any that leave earlier? Or a minibus ? Or cab share?

Ask at the Mukdahan bus station. They have the schedule and if there are any vans headed to BKK they can also direct you to the driver.

There are buses leaving every 1/2 hour to almost everywhere.

You an always fly Nokair pick it up at Ploy Palace Hotel Mukdahan, minibus to airport.

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NokAir and Air Asia both do a Fly and Ride service from Nakhon Phanom to Don Muang. Picks you up at the riverfront or Ploy Palace Hotel.