TypeError in chrony variant

Spotted in ziggy's xymon log:

  File "/usr/share/xymon-client/ext/ntp.py", line 229, in <module>
    offset = do_chrony(bb)
  File "/usr/share/xymon-client/ext/ntp.py", line 170, in do_chrony
    recently_started = secs_since_chrony_started() < 300
  File "/usr/share/xymon-client/ext/ntp.py", line 213, in secs_since_chrony_started
    int(systemd_time_chrony_started.split("=", 1)[1].strip()) / 1_000_000
TypeError: a bytes-like object is required, not 'str'

The test is currently green so I suspect it's a code branch that is not routinely hit - perhaps only when chrony has recently started given the call to secs_since_chrony_started