Canon EOS R3 Advanced User's Manual page 384

Count Up
Rec run
The time code advances only during movie recording. Time codes in each movie file
recorded continue from the last time code in the previous file.
Free run
The time code keeps advancing, even when you are not recording.
Caution
When set to [Free run], time codes are not added to High Frame Rate movies that
you record.
When set to [Free run], time codes will be affected by any changes to settings for
time, zone, or daylight saving time ( ).
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