In New York you can renew it months in advance. My license wasn't due till this month, but I renewed back in June of last year.
NJ shouldn't be much different.
If anything you should go down today and renew it.
From the NJ DMV Web site:
Renewal of licenses
You must carry your valid license when driving, so it's important that you renew your license before it expires. If you do not renew your license for three years or are not allowed to renew because of a license suspension, you must reapply and retake the vision, written and road tests. It is up to you, therefore, to renew your license. If you do not get a renewal form by mail, renew your license in person at any agency. Make sure you take your expiring or expired license, your Social Security number and proof of identity with you. When you renew your basic license, you must also renew the endorsements (motorcycle, commercial vehicle, boat) to drive or operate the endorsed vehicle.
Beginning in 2000 you must convert to the new 10-year digitized photo license when your license is due for renewal. The new license will contain only motor vehicle information and display a tamper proof color picture of the licensee.
If you enter the military and have a valid New Jersey license, renew your license before it expires.