Unless I'm missing something, one always needs an HVACTemplate:Thermostat as part of an EnergyPlus HVACTemplate combination. HVACTemplate:Thermostat objects have the option of defining heating and/or cooling setpoint temperature schedules. One introduces setbacks by altering setpoint values in either schedule.

With the object you are talking about, you have two options, you can either have a constant setpoint or a setpoint schedule.

A setback suggests that you do not have a constant setpoint, which means, as Denis suggests, you would need to use a setpoint schedule instead. There, you could define your setpoint/setback schedule, for example, from 8am to 10pm, your heating setpoint value could be 69 degrees F., and from 10pm to 8am, your heating setpoint ("setback") value could be 64 degrees F.