How did you setup the car to test it? The part about jack stands confuses me - you need to have the cars' weight resting on the suspension to test the valve. I tested mine with the car resting on all four tires.
On my 124 wagon it takes ~2 minutes the fully raise the car when the valve is moved to the "fill" position. The car raises up about 3 inches - it looks *really* funny that way...
Note there is a minimum pressure the valve maintains within the struts & accumulators. (I forget what it is - check your shop manual.) It will never let the pressure fall below this value, no matter how long you leave the valve in the "empty" position. Some pressure is required to insure the damping action of the struts; as well the hydraulic system is partially responsible for supporting the weight of the car. Wagons which are "dragging tail" have lost pressure in the hydraulic system.