unless the xtal on the pic is sufficiently more stable and accurate than the rtc rock its hard to see a meaningful result quickly .have seen clever things done with a gps and the 1 sec pulse the satellite
atomic clock sends out. (described in silicon chip mag , I think it even used a pic chip).
it would probably achieve more to see if you rtc gains or loses time compared to a ntp clock over a period of days (weeks?) and add or subtract 1 (as appropriate) to the adjustment buffer ,then re-evaluate. but in perth weather the temperature difference between inside and outside (hopefully) would probably make calibration doubtful anyway