Your code has a bug in it if you execute it at certain times of the year. You assume that every day has 86400 seconds, but not all of them do.

Change

   # get the seconds since epoch
   my $epoch = timelocal($seconds, $minutes, $hours, $mday, $mon, $yea
+r);

   # calculate the number of epoch seconds since requested days ago
   my $past_epoch = $epoch - $epoch_offset;

   # get the date of X (requested) days ago
   my $past_date = localtime($past_epoch);
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   # get the seconds since epoch
   my $epoch = timegm(0,0,0, $mday, $mon, $year);

   # calculate the number of epoch seconds since requested days ago
   my $past_epoch = $epoch - $epoch_offset;

   # get the date of X (requested) days ago
   my $past_date = gmtime($past_epoch);
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Note that even though timegm and gmtime is used, the result is using the local time zone as you intended.

See Re^2: Get the date (MySQL style) for X days ago for an example of when your code fails.