people are used to the idea, and have been accustomed to, that people's day starts at 6-7am for your normal factory working parent, 8am for school kids and office people, and that the day should end a few hours (4 usually) after dinner (6pm usually?). Parents may be a couple hours later, say 12am?
So instinctually, at 12am even if the kid's not tired, the parent says (according to their schedule) that its time for beddy. Its just always been the way it works for them.
Every age group has their own general schedule. Teens' schedule are more irradical, going out late, movies, boyfriend/girlfriend, sleepovers, etc...
Insomniacs like me and you (those reading at the moment) say "schedule? what schedule?" I wake and sleep randomly. Even when I held an early morning shift (5am) job I never changed. Insomnia got me hooked. Mostly slept at 4am, woke up an hour or so later and headed for work. Come home early at 1 or 2pm. Sometimes I hit the sack in the afternoon when real tired. Other times could keep myself eyes wide open till wee hours of the night, and repeat shift work the next day.
I make an effort not to let "time" control what I do and when I do it, if I have any choice in doing so. What is time anyhow? Its intangible, yet proves to be very significant and plays an important part in many people's lives.
Sure time affects me, but not to the same degree or significance as it does to many others.