My parents have a maid come in twice a week, and before/after special occasions like dinner parties and whatnot. My mother is a doctor, and she stays in her office sometimes until 7-8 at night. Even when she comes home early she is usually exhausted and just passes out right after dinner. My parents have had a maid come in at least once a week for as long as I can remember. They are very happy with the twice a week schedule.
I would suggest starting with having a maid come in once a week, and see how that goes. I think you can even have them come in once every two weeks if that's all you need. Good luck
