How long should the Modulator HOLD Vacuum?

[gmrulz4u]

With regards to the transmissions Vacuum Modulaotor, does anyone know how long it's supposed to hold vacuum?

 

I recently bought a New MityVac Vacuum Pump and applied 16" hg to the manifold end of the steel line that runs down to the Modulator...it only took about 20 seconds to drop back down to 0" hg.

 

I've read times online that vary from 1 minute, to 5 minutes, to indifinitely. I'm not sure if it all depends on what type of Modulator, or if the figures are pretty much universal?

 

Anyone know??

 

THANKS!