Garmin timestamp conversion

Hello, 

I'm still browsing into the Garmin file system and I'm analyzing the "Monitor" folder where there is .FIT files.

I'm trying to figure out how to convert the "timestamp_16" into a regular timestamp value. A topic was open (https://forums.garmin.com/sports-fitness/healthandwellness/f/vivosmart-4/251045/timestamp_16) but there was no answer since a long time... I found some stuff on stack overflow (https://stackoverflow.com/questions/57774180/how-to-handle-timestamp-16-in-garmin-devices) reading that the Garmin timestamp is 631065600 seconds later than the regular epoch timestamp. However, I didn't found a confirmed information about that. 

I was wondering if there was any official documentation on how to handle "timestamp_16" timestamps. If not, is the method described here https://www.thisisant.com/forum/viewthread/6374/ correct ? Or should I also substract the Garmin offset given in the stack overflow topic ?

Thanks for your help,

Richard.