I don't think it's impossible. 1 minute can be a long time. It's differant when someone is working their own job. They move faster and if the screens are started first the energy can be there. When I was cleaning windows, I would always start on the screens first cause I did not tap, tap, tap, tap. I would tap once stright down, then rest the screens below the window to the side. By the time I got the house done the screens would need a quick wipe of the frame and were good to go. My first year I had a large job (80+ windows) the helper I had cleaned the screens in a couple of hours give or take a few minutes. He had a full 6 gallon bucket with solution, brush and garden hose. Once he got rolling he flew through them.
I think kevin said it best in his book. I'm paraphrasing here. But sometimes, it's really not worth going too crazy on things the average customer is never going to notice or care about. Of course you do the best job you can. We all know if we wanted to spend 30 minutes on a window and screen we could get every little stain/debris off of everything and make the window look almost brand new. But when it comes to windows that are neglected like the ones in the photos, any cleaning is going to be a major improvement. When the customer looks at those sills, if they see little bits of stain or debris stuck in the corners they are really not going to care. They are going to be overwhelmed by the dramtic result. Again you try the best you can, but there has to be a time where you stop.