Shorter even that that! Several airlines did operate SFO-OAK-xxx at various times -- I've been on a few of those myself -- and it was certainly was available for sale on the helicopter (and, in many cases, free if there was an interline connection). I believe New York Helicopter offered JFK-LGA service (triangle service among the three major airports, with ever-changing downtown heliports as well).

Pay attention to the original hint, and I'll let you know you have one airport right.