I have it running from a preinit script /programs0/preinit.d/M05ntpdate
Note that /programs0/incar simply returns true if the empeg is on DC power, and is used to quit the script (without running ntpdate) when in the car. incar is distributed in the gpsapp tarball.


#!/bin/bash

([ -x /programs0/incar ] && /programs0/incar && exit
[ -x /usr/sbin/ntpdate ] && /usr/sbin/ntpdate ntp_server)