At any rate, we pulled into the bus station in Harburg just around the time my other bus was supposed to have left. I thought I might still be in luck since my connecting bus is sometimes late, but I think I saw it a bit further down the road.
My suspicions were confirmed when the bus took another 20 minutes to arrive: I had missed the first one because (a) the bus was late and (b) the (already late) bus drove more slowly than usual.
Had I known this in advance, I would have asked the bus driver to radio ahead to ask the other bus to wait in Harburg. As it is, I came to work even later than I already was.