use strict;
use warnings;
use Date::Manip::Date;

my $date=new Date::Manip::Date;

open my $fh, '<', "/etc/crontab" or die $!;
foreach my $line (<$fh>){
    chomp $line;

    #skip SHELL=,PATH=,comment,empty line
    next if ( $line=~ /^SHELL/ || $line =~ /^PATH/ || $line =~ /^#/ ||
+ $line=~ /^$/);

    #skip @reboot,@hourly, etc
    next if ( $line =~ /^@/ );

    my ($min, $hour, $day, $month)=(split(/\s+/, $line))[0 .. 3];

    foreach my $target (\$min, \$hour, \$day, \$month){
        $$target=expand2commasep($$target);
    }
    my $error="";
    foreach my $e_month (split(/,/, $month)){
        foreach my $e_day (split(/,/, $day)){
            foreach my $e_hour (split(/,/, $hour)){
                foreach my $e_min(split(/,/, $min)){
                    $e_min=sprintf("%02d",$e_min);
                    $e_hour=sprintf("%02d",$e_hour);
                    $e_day=sprintf("%02d",$e_day);
                    $e_month=sprintf("%02d",$e_month);

                    if( $date->parse_format(
                        "%Y/%m/%d %H:%M:%S",
                        ,"2011/$e_month/$e_day $e_hour:$e_min:01")){

                        $error.="#############################\n";
                        $error.="LINE=$line\n";
                        $error.="target date/time=2011/$e_month/$e_day
+ $e_hour:$e_min:01\n
                        $error.=$date->err . "\n";
                    }
                }
            }
        }
    }
    if( $error ne ''){
        print $error;
    }
}
close $fh;
sub expand2commasep{
    my ($val) = @_;
    # 1-9 format to comma separated list
    while ( $val =~ /(\d+)-(\d+)/ ){
        my $buff='';
        foreach my $item ( $1 .. $2){
            $buff .= $buff eq '' ? $item : "," . $item;
        }
        $val =~ s/\d+-\d+/$buff/;
    }

    #*/d format to 1
    if ($val =~ m^\*/(.*)^ ){
        if ($1 =~ /\d+/){
            $val=~ s^(\*/\d+)^1^;
        } else {
            print "error: not numeric $val\n";
        }
    }

    #* to 1
    if ($val =~ /\*/ ){
        $val=~ s/\*/1/;
    }
    return($val);
}
[download]

Because you're hand parsing a crontab, instead of using some cpan module to do it for you?