Why not travel at night?

The line they gave in the movie was that it was too dark to see the rough ground. So their original plan was to travel only near dusk and dawn. As they got dehydrated and less coherent, that plan fell by the wayside.

I think that if they had stuck to the road they probably could have traveled at night even with a new moon. I've done that at night.

Exactly right. They should have started walking back on the road they came in on. You can walk at night and in the early morning before it gets too hot. Even on a moonless night, there is enough ambient light to follow a 2-track road. I've done it before many times. These are young people as well, so they could walk much farther and faster than they think they can.

From the moment their predicament began, they made every wrong decision. Stupid, wreckless people do die in these situations. I guess that's the salient message of the film.