40 minutes is bad info, more like 48 hours. Turn your regulator up to about 10psi, when the "hissing" stops, disconnect it, roll you keg back and forth a couple of times (gently), and purge the tank (relief valve) repeat this step twice.
Determine the temperature that your beer will be during carbonation and set your regulator accordingly for the style of beer that it is.
Remember that the gas should be connected to the black beverage disconnect so that the CO2 bubbles up through the beer.
Your beer should become saturated in about two days time, then enjoy!
40 minutes, yeah bad advice.