question, not bug

[Matthew Smith]

i'm using date (GNU sh-utils) 2.0 and i'm not sure if i'd be permitted to
upgrade to another version, but my question is
is there a common way to supply date --date with 'time in seconds since
the Epoch' instead of a YYYYMMDD or similar format?

if so, could you send me an example of correct syntax?
i didn't see anything about it in the man or info docs.

thank you for your time.

sincerely,
  Matthew Smith