How do I convert milliseconds into a timestamp?

[Serapy]

I took this piece from an unencrypted .DAT file:

00 e1 27 17 6f e6 69 c0

Which translates to 63,374,851,375,000,000 in decimal. This number is definitely microseconds.

And this huge number cannot bypass the 1st January 1970 00:00:00 format; such a format that most converters use today.

So, yes. Is there such a converter that uses the 1st January of the year 1 format? Or how shall I make one?

And by the way, a timestamp is both date and time.

EDIT- Sorry, it's microseconds, not milliseconds.

Thanks in advance!