The Delay adjustment 12 o'clock position is 30 minutes moving to 90 minutes at 3 o'clock. If this does not cure the problem or if snow removal is patchy check to see if the deicing system itself is working properly. The sensor relay is closed but the deicing system is not running. In many installations the heating system is supplied by a different breaker than the one supplying the sensor. Confirm that this load breaker is closed.
Some systems also use a high current contactor controlled by the sensor load contactor.
If installed, confirm that this contactor is working properly and that any included thermal overloads are not tripped. Some antenna heaters employee an in-line thermostat for controlling the actual operating temperature of the heater panels.