if you are staying on site for early entry, you'll want to do FJ before it is open to the public.
the wait for FJ and checking out that section of the park will have less peeps in it during the EE period.
usually you will find low crowds, not much on lines in the last hour before the park closes.
you could be taking a chance with waiting until then to try FJ though.
if the ride goes down in the last hour, most likely it won't go back up and you would lose out on that ride.
this past stay i had, did ee for fj a few times.
on my last night, did a walk on for fj.
since i have been on that ride many times in the past, i would have not be heart broken if it was down that last evening i was there.