I would be happy if this helps you:
We had appointment for our FP1 in Hackensack in June 2002.
My wife had to leave the country before the date (similar to yours).
We made a ride to Hackensack before the date just to check our options.
The supervisor has told us: NO, you can't make FP EARLIER, but that's NO PROBLEM: you'd have 90 days starting from the appointment date to perform FP. No re-schedule or appointment necessary, just come any day.
She returned back 2+ months later in August and made FP1, exactly as he said: NO QUESTIONS asked, no problem at all.
So my advise: visit them and check if this policy is still intact. Then make your decision.