A private bus takes around 4-5 hours, with a stop at the caves on the way. We left after breakfast, and arrived after lunch. The drive goes through the national (deforestation) park, Chinese plantations of rockmellon, rubber trees, soybean and mining.
If you are going to LN, put in an extra afternoon (sauna from 4pm) for the best sauna and massage in the world, from the house listed in the Lonely Planet near the fresh markets. We still talk about it. The Talot Sao markets have this really yummy jam donuts cooked fresh and the noodle bar is great for lunch. The night markets in the main street of town have roast pork well worth the stop. You can tell I traveled by my tongue!
The Red Cross runs another good massage/sauna space in HX which employs and trains local people. Nice view from the back deck as your feet are massaged, and you get to wear a fetching outfit, too.