First, how did you get Date::Calc to generate the data file of days? I only ask because when I used those values in this:

#!/usr/bin/perl
use strict;
use warnings;
use Date::Calc qw(:all);
foreach (731158, 731178) {
  my ($year,$month,$day,$hour,$min,$sec) = Time_to_Date([$_]);
  print "$year $month $day $hour:$min:$sec\n";
}
[download]

I see that both are the same date, 1970-10-13.

How about posting some code?