No- with a fully functional vacuum system, the headlights should raise and lower at least once with the engine off even 24hrs later. Not many can do that today, the relays are usually the faulty component and the repros are just as bad.

 

There is a 3rd possibility: The hose connections on the bypass are reversed. I know the OP on this thread has repeatedly said his connections are good, but I don't think they are because reversed connections on the bypass will cause all the symptoms he's described.

If the bypass valve is NOT pulled down, it simply ports vacuum OR atmospheric pressure from the headlight switch to the top hats on the relays regardless of how the hoses on the bypass valve are connected.

If the headlight switch is "OFF", vacuum goes from the headlight switch, through the bypass valve, and on to the top hats of the relays. The relays then direct vacuum to the REAR actuator ports to pull down or hold the headlights retracted.

If the headlight switch is "ON", atmospheric pressure goes from the headlight switch, through the bypass valve, and on to the top hats of the relays. The relays then direct vacuum to FRONT actuator ports to pull up or hold the headlights extended.

A CORRECTLY connected bypass valve, when pulled DOWN, allows atmospheric pressure to enter the UPPER hose (white stripe) connected to that valve, the pressure goes to the top hats of the relays, and the relays direct vacuum to the front actuator ports to pull up or hold the headlights extended.

An INCORRECTLY connected bypass valve, when pulled DOWN, allows atmospheric pressure to enter that valve, and then the atmospheric pressure goes through the check valve, the filter, and into the intake manifold. Hence a vacuum leak; hence a "hiss" at the bypass valve.

To the OP: PLEASE recheck your hose connections to your bypass valve. The white striped hose connecting to the top hats of the relays must be connected to the TOP port on the bypass valve. The blue striped hose connecting to the headlight switch must be connected to the BOTTOM port of the bypass valve.

 

Good relays or holding vacuum? If mine did that its been so many year ago I have forgotten that is how they work.