MB here - 16:30's schedule is very much like what happens in our house. Our nanny works 8-6 M-F. Nap and meal times have shifted over time (as infants have grown into toddlers) but basically her current schedule includes 3 meals (b'fast, lunch, dinner) and one or two naps with playtime, laundry, etc... built in around meals.
On nice days they go to the park/playground, meet other nannies for playdates, etc... On rotten days they bang around like maniacs in the basement.

(Or occasionally she'll take them to the mall to get out or something.)
A lot depends on the families, the kids, the individual family dynamics, etc... I know that our nanny really values feeling like part of the family - being the primary caregiver for the kids and knowing they see her as central in their lives, joining us for dinner or holidays sometimes, staying with us when there's bad weather, being able to count on us for rides when her car is in the shop or helping her move, etc... But that kind of relationship isn't for everyone. In the negative column could be the lack of adult company during the day, the long working days, the pressure to show up since we're all counting on her so much every day, and the fact that she doesn't get paid as much as she might w/ a share situation or multiple families.
So the trade-offs and advantages can be very personal for you. Good luck figuring out what works best for you and finding it!
