The ELC compressor shuts on and off by a pressure actuator , not time related.
Being new shocks, they should stay up all night..Check for leaks, especially where it connects into the rear shock with some soapy water. The coupler you put into the rear shock with the catch pin in it has an O-ring. They tend to shrink and get cracks. A little Vaseline smeared in coupler can help if it the O-ring isnt split. Given the year of your car, the ELC sensor or exhaust selenoid may also be on it'* way out.
This is how the system works: i.e.... Everything you want to know but were afraid to ask about ELC, and I'm feeling gabby this AM.
The Electronic Level Control (ELC) system adjusts rear trim height in response to changes in vehicle loading. This system consists of an air compressor assembly, air dryer, exhaust solenoid, compressor relay, height sensor, air adjustable shocks and air tubing. The compressor is activated when the ignition is On and weight is added to the vehicle. The exhaust solenoid is connected directly to the positive side of the battery, allowing the system to exhaust when the ignition is Off and excess weight is removed.
When a load is added to the vehicle, the body is moved down causing the height sensor arm to rotate upward. This movement activates the internal timing circuit which, after a predetermined delay of 8-15 seconds, grounds pin No. 3, thus completing the compressor relay circuit to ground. When the relay circuit is energized, the circuit to the compressor is complete, allowing the compressor to send pressurized air to the shocks. As the shocks inflate, the vehicle body moves upward, causing the sensor arm to rotate downward. Once the body reaches its original height, the sensor opens the compressor relay circuit and shuts the compressor Off.
When excess load is removed from the rear of the vehicle, the body rises upward, which causes the sensor arm to rotate downward. This movement activates the internal timing circuit which, after a predetermined delay of 8-15 seconds, allows the sensor to complete the exhaust solenoid circuit to ground. With the solenoid energized, air exhausts from the shocks back through the air dryer and exhaust solenoid valve.
As the vehicle body lowers, the height sensor arm is rotated upward until the vehicle reaches its original height. When this height is reached, the sensor opens the exhaust solenoid circuit which prevents air from escaping.
The height sensor position is checked when the ignition is turned On. If the height sensor indicates that it is not necessary to raise or lower the vehicle, the internal timer circuit is activated. After 40 seconds, the compressor will run for four seconds. This ensures the shocks are filled with the proper residual pressure (7-14 psi). If weight is added or removed from the vehicle during this 40 second delay, the air replenishment cycle will be overridden and the vehicle will raise or lower after normal delay.
If the vehicle is staying at the maximum height without the compressor running, you have a bad ELC Height Sensor. If the compressor is running, then you have a bad relay or a short to ground.
The ELC Height Sensor is located on the left rear lower control arm. The Exhaust solonoid is located inside the compressor assembly and also acts as a safety valve to prevent too much pressure from building up.
Hope this helps.