Appsync REST API -- non urgent query

(NOTE: I don't need answer in a hurry, the following is posted just to satisfy my curiosity, however, getting an answer will be appreciated)

Hello,

I am looking at the xml output of a service plan and see last modification time entries in many places within the plan.

While I understand the reasoning behind it but I don't see anything in the AppSync UI that gives me the similar information.

So what is the purpose of such entry? Can it be skipped if one was setting up a service plan as POST operation via xml payload?

If it is required how is the integer value derived in the sample output below?

If I try to convert the number 1459173881907 in PowerShell to date/time format it gives me Jan 02, 1601 date!!!

1459173881907

  Mon 03/28/2016 10:04:41 AM

# $x=1459173881907

# [DateTime]::FromFiletime([Int64]::Parse($x))

Tuesday, January 02, 1601 11:31:57 AM