The Travelfish details at 'Laos 'border crossings' for this crossing are now out of date.
Yes, the bus leaves Muang Khua on the Lao side for Dien Bien Phu on the Vietnamese side at 7:00am (sometimes later, but don't bet on it departing late).
One is well advised to be at the departure point (Vietnamese side of the Nam Ou [river] by 6:30am as the seats on the bus are limited and it's a first come first served basis). As we left, several people were left stranded because they didn't get to the bus site on time to secure a ticket.
Unlike the on the Dien Bien Phu (Vietnam) side, one cannot pre-purchase a ticket.
The price is now 50,000 Kip (with 2000 kip ferry across the river).
At the border, the Laos immigration staff demand a 4000 kip 'processing fee'. You cannot pass through unless you pay it!!!
On the reverse trip, the bus leaves Dien Bien Phu at 5:30am. You can pre-purchase a ticket at the bus station (see LP for location guide) on the day before.
Thanks for the report back Bruce -- I've updated the relevant sections, though I've deleted the duplicate you made in the Laos section, so I can keep the updates in once place.
To add to the above...
The bus is a 22 seat bus that is VERY overloaded - both with people and goods to be delivered. Space on board is cramped. Given this, unless you are amongst the first on board, don't expect a comfortable seat.
The road is not bitumenised. In parts, the surface is good; being crushed stone with clay infill.
There are several river (creek in the dry) crossings.
Sadly, parts of the road are not good. These sections are constructed out of the local clay with very little apparent stone binding the clay. As a consequence, the road is greasy, has long sections of ruts, and the bus has difficulty traversing these sections.
Currently, it is the end of the dry and the start of the wet. The day before we went, there was a storm with heavy rain. The good sections of the road were OK. The clay sections greasy.
I suggest that anyone seeking to undertake this route during the wet season is both a VERY big risk taker, and looking to be 'holed up' for days while the road becomes 'passable'.