It took longer for me to find my Sprint bill (porting number over), than it did activating the iPhone. I'd say roughly 7 minutes or so once I had a copy of my old bill.
I was a bit confused as to how to activate a second iPhone on my plan. The correct way is to use the computer that will be used for the intended iPhone. Instead, I connected it to my computer and did the activation. I then cancelled the sync process and had to rename the iPhone. When I hooked it up to my wife's Mac, I simply chose to erase and sync with that Mac.
Activation of the second plan took 3-4 minutes. Again, the tough part was figuring out how to go about it. When I completed activation of my iPhone, it would have been great to receive directions on how to activate the second iPhone considering I had selected the Family Plan.
Overall, I was happy with the activation process. Going forward, I'd prefer to do it this way, then have to call in and deal with customer service (ala Sprint).
-Chris