I work in the office 3 days a week (or about 24 hrs/week). I make hospital rounds 2 days a week, roughly 2 hrs. each day.
Then I share call with 2 other people. Roughly 12 days a month of 24/7 call. Most of our ladies go into labor at night
Other places probably do things a bit differently.... but I do earn my keep with an average of 6-7 babies born per midwife per month...