Gregorian timestamp - how to convert this to readable format in JavaScript

I'm currently building a React application for a take home assignment for a job interview and I'm currently stuck on a timestamp that I have not seen before.

  {
    "type": "motion",
    "startTime": "637703442050000000",
    "duration": 2000,
    "eventId": "d2faf37d-6fb4-40b3-996c-1703044c724e"
  },

I've search the web last night for hours to be led on different paths but I'm still stumped on this. Any kind soul of there that can shed some light on the startTime entry. I need to convert this timestamp so that I can do some calculations on event lengths.

Edit: it's an 18 digit number for clarity

Thanks :)

Apologies - just read some more information that I did not see

Dates/times are expressed in ticks, that is: the number of 100-nanosecond intervals that have elapsed since January 1, 0001 at 00:00:00.000 in the Gregorian calendar. For example: 637703442050000000 is equal to 2021-10-20 16:30:05. Durations are in milliseconds.