My fuel system will sometimes hold the fuel pressure for several days.  But, it will always hold the pressure for 30 minutes or more after turning off the fuel pumps and injectors.  So it sure seems something is continuing to let the fuel into the chamber after you have turned things off. 

 

As I recall; when I turn the pump off, with everything else off, the pressure decays down to a few psi within a few minutes.  My engine always starts pretty much instantaneously, so I don’t think that is an issue.  I presume there is a slight bleedoff of fuel through the regulator, but in any case, it would take very little to drop the pressure unless you have lots of stretchy fuel line.

 

Al