I rarely use my foam cannon/PW anymore. Its just too much work bringing it out, plugging it in, untwisting the hose and my Karcher is so top heavy that it falls over. Also keep in mind I have a full size crew cab pickup.
The only time I will bust it out is in the winter time if its above 40 degrees or so and I have salt on the truck. It will take me about 2 + hours to wash it depending if I clean the fender wells, wheels, tires etc.
I used to use my foam gun by foaming it up panel by panel but I've come to realize that IMO it still takes too much time.
So all I do now is rinse the whole truck with water, then foam the whole truck with my foam gun then continue with 2 bucket wash. Now it takes me about an hour for everything, including the drying process. If the sun is out and hot I'll foam the whole truck a few times to keep it wet with soap. Helps with water spots.