I run a raspad3 with a build-a-pi/73linux build on it.
Usually sync my time via wifi before I leave the house. Sometimes had to reset the time by hand ( date function and phone) when I noticed it had drifted. So,etimes it got better, sometimes it got worse. Now I am updating the time with GPS update command from the the phone via the Hotspot.
I did the chrony mod you suggest Monday morning. Haven't had a chance to try it out yet as my POTA time is on the weekends and nothing set up at home currently.
I'll post sometime this weekend what I notice. I am planning to setup the 70cm stuff to test out this Saturday night.