The scheduling program breaks the 24-hour day into 4-time periods: Morning, Day, Evening, and Night. If you make a manual adjustment to the temperature during one time period, the thermostat will go back to the programmed set point when the next time period starts. In other words, the override only lasts until the beginning of the next time period. Hold Until will display on the physical thermostat, indicating how long your temporary target temperature will last.
Ex: Your night temperature is set to run from 10 PM to 6 AM. At 3 AM you adjust the temperature setting. The thermostat will now run on the new setting until 6 AM when the next schedule period begins.