The time is stored in UNIX time, which is the number of seconds that have elapsed since January 1, 1970 UTC.
So, you basically have 8 years minus three days. Which is ((8 years-3 days) * 365.25 days in a year * 86,400 seconds in a day) = 252,201,600
Now, this is slightly off since I have no idea what time you actually posted that date data. But, it’s close enough to show you how it’s done.