Is it normal on the LT1, for the fuel pressure to "bleed down" to zero after the vehicle sits for a couple of days?

 

I'd say yes. The pressure won't last forever.

 

Is there a typical length of time that the system stays primed?
Want to eliminate possability of leaking injector.

 

If you think it might be an injector, then pull the fuel rail, put a piece of cardboard under the injectors and prime the system. Let it sit for a while unless the leak is obvious.

 

I would think if an injector were leaking you should be able to tell from looking at a spark plug (one plug would be darker than others) or is running noticeably richer at startup. I had fuel pressure leaking down in my car immediately after I killed it, turned out the fuel pump was going out and that was the first sign. Had to let it crank for an unusual amount of time while the fuel pump primed the line. Put a 255lph in it and it’s been good.

 

If your car is holding pressure for even 5-10 minutes then I would say your fuel system is fine. But as states simply pull the rail up high enough to where the bottom of each injector is visible and prime the car by turning the key into the run position. If you have an injector leaking it will be visible at that point by dripping or spraying.

 

Leaking hose on fuel pump outlet can cause pressure leakdown, too. Mine basically will only hold long enough to start the car, but is fine when running.