Depending on the type of cage you use, I agree with lane_m about covering the cage. If it's a well ventilated cage, this is a good option--but it is not something that should be used if it's something not well ventilated like an aquarium (don't know your cage type, just throwing it out there).
You should try to stay consistent and cover the cage at the same time each night, then uncover when you sleep or when it's time to leave for the morning, whichever comes first (I'm also a college student so I know how those hours go--senior year, woohoo!
). That way it gets dark at the same time each night and light can get in when morning arrives.
A lot of people have tried this method and it seems to work for them.