I'm working with a Drupal 8.3.6 setup done by someone else and I have a date format that doesn't make sense to me. I'm interacting with it thru MySQL Workbench. The best I can tell, 1499287512 = Wed, 07/05/2017 - 23:02 and 1501079338 = Tue, 08/22/2017 - 06:25 BUT there's no guarantee of that. In any event, 1499287512 and 1501079338 appear to be in a date placeholder; numbers like it appear in users_field_data.fields, created, changed, access, login.
Those are dates stored as Unix timestamps, which are essentially the number of seconds since midnight, January 1st, 1970 UTC (the epoch is 1970-01-01T00:00:00+00:00).
As far as Drupal is concerned, they are proper fields on those entities, either
Keep in mind that the timestamp always refers to that epoch and always is referenced to UTC; there is no real thing as a Unix timestamp in a local time zone. When working with them in Drupal it is always best to use
DrupalDateTime objects, and use it methods for computation (which will inherit from