That last _gmtime() implementation should read:

sub _mktime {
    my ($time, $islocal) = @_;
    my $class;
    if (ref $time) {
      $class = ref $time;
      $time->[c_epoch] = undef;
      return wantarray ? @$time : bless [@$time, $islocal], $class;
    }
    if ($time !~ /^\d+$/) {
      $class = $time;
      $time  = undef;
    }
    else {
      $class = __PACKAGE__;
    }
    my @time = $islocal ?
            CORE::localtime($time)
                :
            CORE::gmtime($time);
    wantarray ? @time : bless [@time, $time, $islocal], $class;
}
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Matt