The reason I chose the 5:30 - 6:30, 1 hour session was to try to make the study group as accessible as possible.  Instead of dedicating an entire evening, someone can say to an "understanding" spouse:  "Hey I'll be a little late for dinner".  Beyond that though I certainly have no opinion on whether we should have topics that span multiple weeks.  I think that's  something  that we'll discover between now and Christmas.