`/dev/ptp0` and `/dev/pps0` magically showed up and yeah, it appears to be stable. Chrony actually has it marked as a non-false ticker atm and is marked as a backup. Here's the stats:

  Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
  ==============================================================================
  PPS                        64  40   67m     -6.827     33.059    -72ms    99ms
  PTP                         6   3    20     -9.585      0.005   -119ms    10ns
  192.168.100.1               6   3   88h     -0.159      0.000    -12ms  3815ns
  192.168.100.2               6   3   29h     -0.176      0.299    -11ms  2817us
  ntp1.hetzner.de            14  10  154m     -0.003      0.006    -47us    12us
  ntp2.hetzner.de            11   6  103m     -0.001      0.005    -21us  5711ns
  ntp3.hetzner.de             9   6  137m     -0.006      0.007    -72us  8949ns

I don't feel great about sharing the discovered stratum 1's on the open internet, but my email address is in my profile.