Run

$ bakasync init      # write the config file, say where the key goes
$ bakasync doctor    # check config, key, timetable, calendar
$ bakasync --plan    # print what the next sync would change, write nothing
$ bakasync --once    # sync once, ignore the interval
$ bakasync           # sync on BAKASYNC_INTERVAL, or once if unset

doctor and --plan never write.

Set BAKASYNC_INTERVAL=10min to leave it running. Otherwise it syncs once and exits, which is what you want under a timer or cron.

--config <path> works on every command, so one machine can drive two classes:

$ bakasync --config ~/.config/bakasync/sister.env --plan

On NixOS the module runs it as a systemd service. Elsewhere, a timer or a --once cron line is enough.