It'd be useful to know exactly how low the temperatures get in the room. If there's no thermometer, you can buy a cheap one and use it to monitor the room for a few days. I have one that records the lowest and highest temp each day, for about $10.
If the room stays at or around 60F, there shouldn't be a need to take any steps, except adding lots of bedding and nesting material so your hams can curl up comfortably
generally they'll sleep through the day, so a bit of cool weather shouldn't bother them as long as it's not dangerously cold.
If it gets much lower than 60F, then you may consider leaving the heating on at a low level during the day. If you have tank cages, a great option is to buy reptile tank heaters; the stick-on kind that go under the tanks, and placing them on the side of the tank where the hamsters sleep. These are self-regulating, and placing them on the side allows the hamster to move away if they become too warm.