#!/usr/bin/perl -T

use strict;
use warnings;
use Archive::Zip;

my $zip     = Archive::Zip->new("file.zip");
my $members = $zip->members();

my $firstdate;
my $lastdate;   # No need to fill these in with "never", because I have had dates before.  ;-)

foreach my $member (@members) {
  my $filedate = $member->lastModTime();

  if (($filedate < $firstdate) || (!defined($firstdate)) {
    $firstdate = $filedate;
  }
  if ((!defined($lastdate) || ($filedate > $lastdate)) {
    $lastdate = $filedate;
  }
}

$fh->close();

# Calculate the difference between the first and last
# file dates...
my $datediff = $lastdate - $firstdate;

# Check if the time difference between the first and last
# files is more than 3 months...
if ($datediff > (60 * 60 * 24 * 30 * 3)) {
  # You need a new file
}