Opens On Sunday

I have been doing Open Houses for a number of years now and I have been seeing something happen. Some companies(my own included) have cut back on the Open House hours (ex. 1-3 etc.)Some have changed to different days (ex. Sat from 1-4 etc.)has anyone found any success in doing them any other days or shortening the time period? What is the advantage in that? Please let me know. As always I look forward to hearing from you.