A little over 2 hours work is horrible. People posting above are right that if you have attained your seniority, whatever that duration is at your center, then you are by contract supposed to be given 3.5 hours a night. If they try to send you home early, go above your immediate supervisor if you have to and ask if they need you somewhere else in the building. At the hub I work, it is not uncommon to be there beyond 5 hours, but there was one day in my training period they asked me to leave early because my belt was slow. I asked the management for work somewhere else and they had me busy for almost 5 hours that night loading other belts. Just because your area is clear or slow and they want to send you home doesn't mean there isn't something else for you to do. Take advantage of other people leaving and take initiative to find work if you want more hours.
-k