It depends on the temp of the beer and the desired level of carbonation.
So for 2.5 volumes at 38*F, you can set the regulator to 12 psi and leave it alone for 5 to 7 days.
To get the same result at room temp (ex 60*F) would require 25 psi.
I speed it up by shaking for 30 minutes at 30 psi and 38*F, until no more gas will go in.
The pressure will drop until it reaches equilibrium, then I add CO2 at 12 psi for a day or two until it's steady.
Just my .02.