More than the time it takes to turn it off again should be sufficient - that's if you've pre-lubed up - anyone for KY?
But seriously, I'm listening!!!! Nope can't hear a squeak.
However really seriously, with an engine pre-primed, any non-movement of your pressure gauge seconds after firing is not right.
Fill it to full
oil level, crank it only numerous times and check your gauge during cranking. Should get some pressure even during cranking!! After that I'll wait for the roar.