I crossed over Nong Khai and on to Vientiane in May.
What you're likely to encounter - no problems, just a long wait (take water); get your Laos visa there,
Doesn’t pay to be in a hurry. We arrived at 4.30am and joined the queue of people already waiting for the Thai Immigration to open at 5.30am. Very slow process of getting visa for Laos; then a bus across the Mekong to the Laos border checkpoint, more delays and finally on the bus to Vientiane at 9.20am - almost five hours.
Maybe arriving later in the day is a better idea, early morning there was a huge queue of trucks, people, already when we arrived on overnight bus.
On the way back (a Friday afternoon), arrived 1pm and was on the Thai side 2.50pm.
Since you're already there . . . Vientiane's a nice relaxed place to spend a couple of days.
As you already have a
Double Entry Tourist Visa, you have that part sorted, but for anyone else referring to this thread, another option for a four month stay for a US passport (and any G7 country USA, UK, Spain, Germany, Poland, Italy, Canada) would now be a
Single Entry Tourist Visa as follows:
SE TV = 60 days
Extension at any Thai Immigration regional office (not border) = 30 days (fee 1900 baht)
Crossing at any land border = 30 days for passport holders from G7 countries (listed above), remains at 15 days for others
At the border