Boost leak..How long should the system hold the pressure??

[JoEgsX90]

I was wondering durring a boost leak testt how long should the system hold say you dump about 20psi into it and turn off the compressure how long should does it take to go down?

 

[gofer]

... if you can build 20psi solid on your car then more than likely you have no boost leaks. the system is usually pressurized for 15-20 seconds but not at a solid 20psi, it slowly drops.