Alan,
The house you described would normally be done in no more than 10 minutes with a ladder, ditto a WFP, that is quite a small account.
I do one of a similar size (bottom of Thornwell Roger, just behind the mini tesco place)
4 windows upstairs, kitchen window at the back plus large double patio doors.
Front door (half georgian) small toilet window and 1 other window to the side of the front door.
Windows are wooden, varnished and have 2 panes of glass per window.
Time taken, just over 6 minutes to clean, and another 2 mins to unload and then pack up, 8 minutes in total (timed). and that included sitting in the car to write out the invoice too.
And I charge £8.00
Ian