[derefr]

Mayhap it's simply an artifact of social psychology: if you're working later than 6pm, everyone else is off work and out having fun, and you're cloistering yourself with your work when you could be out socializing. (Even if you'd rather not.)

If you get, say, stationed on a submarine doing night missions, the group you'll mostly be socializing with suddenly gets off work around 7AM. The urge to keep to a 9-5 fades quickly.

[sophacles]

I think there is really something to this - I barteneded my way through college, and for a couple years after (in order to travel and take care of some youthful exuberance that was incompatible with a standard job). As a result, my "money shifts" were Thursday, Friday and Saturday nights, and my days off were typically Monday and Tuesday. A lot of my friends and social circle were in the service industry as well. As a result when I decided to do the career thing, it took several years to get over "Tuesday is a day off" and "Saturday is super productive" type thoughts. Similarly, I still find evenings to be more conducive to work than mornings because my schedule was bar hours - 4 or 5 pm - 3am, and relaxing after work makes no sense, I prefer a relaxing, slow start to the day.

[mercer]

I jumped straight from being a student to being a freelancer, so I didn't really experience 'normal' work hours until much later (as a contractor working on location).

I found that I did slowly gravitate to normal hours because of precisely this reason. My friends started having regular jobs and so I ended up having to adjust my working hours to that.

In fact, I was worse off because I didn't really realize I was conforming to normal work hours, but clients realized that they could approach me whenever they wanted, which was usually in the evening or the weekend.

It took me a while to learn how to not answer every email or phone call at odd times, and re-condition my clients.