The entire process, from having your application approved to scheduling your interview, can take anywhere from 2 to 6 months depending on how booked up your local CBP office is with interviews.
To expedite this, you might be eligible for Global Entry Enrollment on Arrival, which allows Global Entry applicants who are conditionally approved to complete their interviews upon arrival into the U.S. at eligible airports. This eliminates the need for you to schedule an interview at a local enrollment center to complete your interview process.