i did it last year. same as you ti 29er , normally do the 100k but did the 2 x 50. the night route is similar to what you would expect from a merida day route , a mix of road , double and singletrack. quite a good atmoshphere and looks quite good at times when you can see lights zig zagging up and down hillsides.
top tip. dont drink too much energy drink or gels on the night ride or you wont get any sleep before the morning :-)