I just learned of a better way to do this:
All GoPros with GPS store a DateTime in UTC from as part of the GPS Data.
We can use this data to overwrite the Exif data…
exiftool -overwrite_original -r "-AllDates<\${GPSDateTime}" /FOLDER
… and then manually fix the offset to UTC wich is 2h for me ATM
exiftool -overwrite_original -r "-AllDates+=0:0:00 2:00" /FOLDER
Those commands also are recursive (-r) and overwrite the existing file (no *_original files anymore).
In order to validate the times, use this command to get all the different dateTime values for a file or Folder
exiftool -DateTimeOriginal -CreateDate -ModifyDate -GPSDateTime -r /FILE_OR_FOLDER