Convert date to a timestamp

I am trying to analyze a website and I'm having hard time to understand how the date is being converted.

For example choosing the date :

08 March 2019 is being converted to 636876000000000000

9 March 2019 => 636876864000000000

10 March 2019 => 636877728000000000

I thought it's timestamp so I tried converting it online but it doesn't give the correct result.

Any ideas would be much appreciated.