I don't know, I found for me that it was more of a psychological barrier than anything else to biking longer distances. One time on a recreational ride I took a detour and ended up biking 22 miles. Once I did that, I realized that if I worked a bit more, I could make a 26 mile RT grocery run with a trailer. So I biked 41 miles one day, without a trailer (though I did sorta bonk and had to stop for food), and figured I probably have the strength/endurance to do this grocery trip.
Then again, I wasn't horrendously out of shape to start or anything like that.
Biking in the dark does not sound fun, especially in the woods! I bike at night on occasion, but on reasonably lit city roads.
Incidentally one of the people in the cycling challenge said he almost ran over a deer. Or was it the other way around? =)