@Michael *******
usually because of the flights to Vientiane you are compelled to spend 2 more nights in Lao. That's because the flight doesn't arrive early enough to get to the consulate before they close and the next day it departs before you can get your passport back.
The fly to Udon, bus to Nong Khai, cross and make your way to Vientiane is about the best way to pull it off.