Eric,
I'll ditto the advice the previous poster gave you. Just keep checking the appointment schedule on line for new availability of appointments.
Our original interview appointments were months out, but by "stalking" the web site a few times each day, I was able to snag appointments such that we were finished with the whole process within a month....start to finish!!
One of the homeland security staff actually recommended I do that, since it is apparently quite common for people to have things happen in their lives that require rescheduling of their originally scheduled appointments. But, the rep warned that for couples to snag earlier appointments, it would likely mean separate dates for each person's appointment, as was the case with us.
If you are somewhat diligent in checking the appointment scheduling site, you'll probably be all finished and good to go within a month or two.
The demand for Global Entry has obviously gone up, as more and more people see the 3+ hour TSA lines on TV, thus the longer waits for the interview appointments. Supply and demand issue, coupled with staffing budgets.