[jackpirate]

I figure that around noon in the US is the largest traffic, so you will spend less time on the front page as more articles are submitted. But that time is more valuable because more people will see it.

Conversely, if you post at midnight, you will get more time, but the time will be less valuable. So in the end, I think it probably evens out to the same number of users visiting an article.

The trick (not that I'm a big submitter) I would guess is to post things at all hours. I imagine many people have a habbit of only cheching at a certain time. Maybe it's their lunch break, maybe just before going to bed. By posting things at all hours of the day, you can reach all of HN, rather than just the subset that visits only at certain times.