Sorry for the long delay, I got frustrated with this device and put it away for a few weeks.
Unfortunately it is not the clock. I loaded the latest OpenWRT trunk build on it and set the clock, installed packages, and generally tested the device. As far as I can tell the hardware is fine. I also have a new 2GB SD card to remove any possible concerns over the microSD adapter or the SDHC card I had tried with previously. The machine has not been unplugged since the OpenWRT install was running, I just rebooted it and ^C'd in to redboot to start the pfsense install, so the hardware clock has no reason to have lost its setting.
I still can't flash pfsense1 and it still pukes when trying to mount the root, then stalling at the same t_delta messages as always.