In Secondary School, you have assigned classes throughout the day. The classes usually start in the morning and end sometime in the afternoon.
In College however, class times are much more flexible and random. Some students may have class at eight o'clock, while others may not have their first class until ten or eleven. There are also large sections of time between some classes. For example, on Tuesdays, my first class ends at noon, and my next class doesn't begin until two o'clock. After that one hour class, I am then done with class for the day.
Even though having flexible class times is good, it forces you to become a much more responsible person with time management. The varying times of classes is a huge benefit of college, because if you pick the right times, you don't have to get up until ten or eleven each day. Because of this, many students don't go to sleep until very late, and at two or three o'clock, you will still find people watching TV or playing on their computer.