It is possible to change a hamster's sleep schedule. It's not easy, and it may not be permanent, but it's possible. We're speaking here about Syrian hamsters, which must be kept in cages by themselves. Dwarf hamsters will respond similarly, but their behavior may be affected by their cagemates, and thus may not be as readily changed.
A hamster's behavior is mostly determined by the environment and repetition. The Syrian hamster has been kept as a pet for less than one hundred years. For perhaps tens of thousands of years prior to that they each lived in desert burrows, alone, responding only to their personal survival needs and the weather, which, being on a desert plain, hardly changes. So when a Syrian hamster enters your home, he or she is carrying on the kind of activity that's written into its DNA. That's the long way of saying hamsters are truly "creatures of habit."
The key, then, to changing a hamster's wake/sleep schedule is to create a gentle transition in the way their day goes. Remember that "personal survival needs" mainly involve getting food. In the wild this activity is initiated by the hamster, which has a sense that it should go out every day and gather things. But in your home, you're the food source, so you must create a pattern to imitate nature.
To do this, toss away the food in your hamster's dish and replace it at a set time daily. There's a side note here: Your hamster’s diet is a separate subject altogether, but in short, it's not a good idea to limit it to a store-bought mix, and to simply refill the supply when it gets low. First, the hamster will eat what it wants, and leave what it doesn't, which may lead to malnutrition. Second, grains oxidize and lose their nutritional value, and the oils become rancid. Finally, fresh foods provide a wide variety of active nutrients, and hamsters like them, so they offer a good incentive for training.
With that said, back to "time-shifting your hamster": Take note of when your hamster typically rises in the evening, and set out a dish of food around then. The dish should include some fresh items for the reasons above, and because these send an aroma signal to the hamster that reminds it of its need to "go out and gather." Set the dish near the cage if your hamster is sleeping soundly so the smells can trigger your hamster’s wake-up call instead of startling it by placing it in the cage. Your hamster will see this as a focal point of the day, and it will begin to order its activities around it — eating, running, grooming, napping and so on. It's like a delicious, life-enhancing alarm clock!
If you're truly consistent, meaning that you perform this food change at exactly the same time every day, it will take most hamsters only a week to get a fix on it and react consistently as well. Then the process is simple. Just move the time you do this up or down by 15 minutes every five days or so. Again, you're going to have to be very, very regular about it. This method has been known to change a hamster's sleeping and waking time by as much as an hour over the course of a month.
Please note that when we change our clocks for daylight saving time, if that applies to you, we're sort of doing the same thing to ourselves. Our hamsters, in turn, will react to changes in our activity, light and dark, noise level, and so on. That will also alter their waking and sleeping patterns.
Eventually your hamster may just wander off the schedule for reasons that can't be explained except to say that occasionally doing the unexpected is one reason we love hamsters so much
