Since it's not in production yet, I just boot it when I'm tinkering with it, then shut it back down. However, this error seems to have gone away since I fixed my fstab entries the other night (pfSense was originally booting off /dev/d1s1a because it was installed from USB stick, but after removing the stick, it moved to /dev/d0s1a because of the way my BIOS handles USB devices as hard drives). Not sure if that was the underlying cause, or just coincidental. Now OpenNTP goes through its thing in like 5-10 seconds.
Also, at one point I had the box running with a USB NIC too, but switched over to the onboard and had left the configuration the same between the two. I finally unplugged the USB NIC the night I did the fstab thing, until I'm ready to use it again… so I'm wondering if maybe OpenNTP was trying to route over the (not-connected) USB NIC.
Anyways, it seems to be behaving for the time being :P