Problem Statement

Choose popular date libraries used by your language and show the   epoch   those libraries use. A demonstration is preferable   (e.g. setting the internal representation of the date to 0 ms/ns/etc.,   or another way that will still show the epoch even if it is changed behind the scenes by the implementers),   but text from (with links to) documentation is also acceptable where a demonstration is impossible/impractical. For consistency's sake, show the date in UTC time where possible.

Let's start with the solution:

link printf,datetime

procedure main()
  # Unicon
  now := gettimeofday().sec
  if now = &now then printf("&now and gettimeofday().sec are equal\n") 
  printf("Now (UTC) %s, (local) %s\n",gtime(now),ctime(now))
  printf("Epoch %s\n",gtime(0))
  # Icon and Unicon
  now := DateToSec(&date) + ClockToSec(&clock)
  printf("Now is also %s and %s\n",SecToDate(now),SecToDateLine(now))  
end