Yeah, I tend to agree with you about riding farther. Night starts really throw things off. It really depends on how you are riding and if anything hurts or you are too sleepy. I certainly wouldn't want to stop with daylight left, probably not before 9 or so.
I was really sleepy on the 400k I just did, but it just goes away in an instant for me. It doesn't help when your riding companion lets out a yawn -- instant sleepiness. I'm good for the first 25 hours at least, but I have a lot of practice from very slow 400k's.