There was a discussion about this on a separate forum that I belong to, and most orgs seem to go by the 3hrs a day rule of thumb, regardless of the number of fosters in the home. We've adopted the 3hrs a day for fosters as well.
------------------------------
Erin Ellis
Community Engagement Director
Humane Society of Truckee-Tahoe
---------
Foster Program & Volunteer Management Specialist
------------------------------