We played Black Fang last night after getting the beginner box. I opted to start the PCs in Sandpoint at the Rusty dragon to start introducing them to the town. They got the info for the 'hunt' off he help board in the inn and had to go speak with the mayor to get the full info and officially accept the 'hunt'. That added a bit to it both time wise and in player/ncp interactions. We played for 5 hours and they died right before the end (lol) so we are finishing up today. If you stretch and pad it a bit it is defiantly enough for a full session. I Was worried at first about that as well. After BFD we are going to do the deadly mines with an add on attachment from one of the wayfinders (into the dark wayfinder #9). Wayfinder #9- into the dark, the gateway to the nar voth, and Deverins folly-has a lot of good ones that go well with the beginner boxas does wayfinder 10,11,12 and that I feel will be a good follow up. After we have done some of those and I feel we all (me as a GM and they as players) have enough experience to really start an adventure path we are going to start Rise of the Ruin Lords. I am a new GM but the things I listed give me every thing I need to make a worth-wile game that has good content all around.
Yes, the Beginner Box does a great job of introducing pathfinder.
If you want to stick with BB adventures for a while, Ed O War has converted loads of other classes and creatures to Beginner Box rules.