I'm sorry if this is miscategorized. How would I best get from Udon Thani (Metropolitan) to Laos Airport, and how long should I budget, conservatively?

Minivan (or taxi, but won't be much faster) from Udon to the border, takes you about an hour.

Stamp out of Thailand, bus over the bridge, apply for Laos visa on arrival and get stamped in, about 30 minutes.

Taxi from border to the airport, maybe 45 minutes.

So it should be possible to do this in about 2:15 hours, but obviously you should add some more time as a buffer, maybe there are many people at the border, traffic jam, or whatever.

Because i don't like to get stressed on my way i would start this journey 5 hours before the flight.

Thank you, JackDD, top-notch!