Hi Santino,
It's hard to say how long a property should take, a lot can depend on the access, style of window, type of frame material, frequency of cleans, local conditions causing the dirt etc.
For a similar house, I'm guessing I would be charging around £12 to £13 - more if there's french doors, patio doors, conservatories or porches.
So even at £12 you would comfortably do two an hour. Try to get into a routine on every clean and every window - particularly on the maintenance cleans. Hose out to the furthest point and work back. - If you could shave 5 minutes of your present time - you could do 3 an hour - happy days - just don't cut corners.
Good luck, Dave