As said before its the time the bolt inside the gun will stay forward and allow air to pass thought the breech, in turn controling how long the cycle takes. Too low of a dwell the gun will not cycle fully. Too high of a dwell, the gun will eat through air and be a gas hog.
As to find out the stock dwell setting, look in the maual around the board programing section, it should show a chart and it will tell you what the stock dwell setting is. If you dont have a manual, just google "(gun name here) manual) and one should pop up
good luck my friend