Sometimes I'm silly. Noticed that a fire camera I was watching showed a clock over a minute ahead of my system time, assumed the problems was me. Installed Chrony (Linux Mint, recent Win convert so I'm hardly a power user) and spent the usual 20 minutes farting around with it. Couldn't seem to get it right.
Finally realized my clock IS within a handful of microseconds of the NTP server; it's the clock on the camera that's wrong. D'oh.