Rotational (again) - how long per house?

I usually play a household until I reach a certain goal for them or, if it's a long term goal, I get tired of them. I could never play for one day and then move on to another household. Because of this, I tend to group together sims with similar interests, so if two of them are into gardening they will call each other up and garden together. If I know a sim is collecting something, I will call them up and gift them a piece for their collection. For fun and friendships they usually hit the bars together. If you wish to harvest vegetables you could do so in a community garden.