What about (untested...):

sub process
{
  my $mtime = (stat($_))[9]; # moved this line up
  return unless (/\.html?$/ && ($mtime < 946684800));
  $ct++;
  print "HTML: $File::Find::name\t\t";

  ($seconds, $minutes, $hours, $day_of_month, $month, $year,
  $wday, $yday, $isdst) = localtime($mtime);

  printf("%02d/%02d/%04d\n",
  $month+1, $day_of_month, $year+1900);
}
print "Tot = $ct\n";
[download]

NOTE: 946684800 is the epoch time for Sat Jan 1 00:00:00 2000 GMT which I found thus:

perl -MDate::Parse -e"print str2time('01 Jan 2000', 'GMT')"
[download]

HTH!

--
Cheers, Joe