The hours all depend on your line of business. One of my friends is a presenter at Innoventions East and her hours are usually 10am-7pm. Merchandise has different hours as well. Sometimes I get the morning hours from 9am-4:30pm, and sometimes night hours, such as 3:30pm-midnight. In addition, it can also depend on the internal workings of the location. When I am doing registers, it is usually 6 or 6 1/2 hours, but this past saturday I was doing floor stock, and my shift was 8 hours.
Times change when it comes to minors. I'm still considered a minor even though I am 18 because I still go to school. Saturdays and days where there is no school the next day, there is no restriction to how late, but if there is school the next day then the hours are limited up to 10:30pm.