As a general rule, the recommended heater temperature at night is between 60 and 67 degrees Fahrenheit. A thermostat setting of around 65 degrees is actually better for your health. Again, your optimum nighttime temperature will vary based on your preferences.
Reducing the temperature overnight can provide additional energy savings, but finding a balance between those savings and the extra energy your system uses to recover in the morning can vary. This can vary based on the outside temperature, how your home is insulated and the specific system you have.