In unlocked mode, if the thermostat is run without setting the time the override will run until manually changed or until the clock is set and schedules start running.
In locked mode when the thermostat is run without setting the time the override will last for the duration of the override timer (set in the basic configuration). The default override timer is 8 hours. Once the override timer has expired the thermostat will revert to the non-override manual setpoints.