The optical heart rate settings message tells whether the wrist heart rate sensor is enabled.
Moment the message refers to, in UTC. FIT stores it as seconds since the FIT epoch (December 31, 1989, 00:00:00 UTC); decoders usually expose it as a regular date.
enabledEnumState of the optical heart rate sensor: on, off or automatic.
autooffonmesgNumStringGlobal message number identifying the kind of message. Decoders use it to know which profile to apply to the data.