You're probably looking at it the wrong way...

EnergyPlus uses thermostats that are ideal, meaning that provided that you have HVAC equipment available with sufficient capacity, your thermostat will be respected at all times. For eg, if you define that you have a heating thermostat setpoint of 20°C from 9:00 to 21:00, and 18°C from 21:00 to 9:00 the next day, that's what you'll get.

Your "smart" thermostat is somewhat trying to provide controls that approach this ideal control. So the question is more how you need to model your case without a smart thermostat... And the answer to that is up to you, but could include for eg the following:

• You could model a lack of setback, or a setback not aligning with occupancy. Smart thermostats usually have an occupancy sensor, so they'll go to "setback" mode when it's not occupied. It also tries to learn your usage patterns so it will start bringing your building back to setpoint temperature before you return. On the other hand, regular thermostats are either fixed temperature (+manual utilisation, eg occupant may decrease the setpoint as they leave and bring it back up when they return) or can be programmable (you set a schedule... but do you do that correctly? How often do you revisit your schedule to adjust with your changing lifestyle...?)
• You could model overheating / overcooling during non setback times due to more manual input needed.