Being unfamilar with pitch, I think I may have misunderstood your request. Are you playing rotating partnerships? If you go to the schedules link above and then dial up Whist for 20 players, is the 19 round schedule the type of thing that you are looking for? My reading is that you want 4 rounds per night for 10 weeks, so two copies of the whist schedule is going to give you 38 of the 40 rounds.