Convert timestamp 16 to date

Hi everyone, 

I am doing a project were I will need to combine heart rate data with an external dataset of other medical factors and I need to get the exact datetime of the dataset. In the developer page it says that the timestamp_16 column corresponds to date since 1970, however when I get the data I get a few thousand seconds, corresponding to hours not decades. How can I get the correct date and time for each heart-rate measurement?