Your code is a good example of why "use strict;" is a good thing. I would recommend you adding it to all of your code, it will help you debug it. Here is your code fixed... see if you can see the differences:

#!/usr/bin/perl
use strict;

#$myname="Merlin";

my $DEBUG = 0;

# my added here
my $timediff = 0; # ?

my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime (
+time + ($timediff * 3600)); 


print "$mon $hour, $mday, $mon, $year, $wday\n" if $DEBUG == 1;

my @months = ('01','02','03','04','05','06','07','08','09','10','11','
+12'); 

my $month = $months[$mon]; 

print "Content-type: text/html\n\n"; 

if ($month eq '11'){   # use 'eq' to compare strings  Nov eq '10' btw
    undef $/; 
    open (FILE, 'hours.txt'); 
    print <FILE>; close FILE; 
}
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1) Comment your code
2) Place debug print statements in, or learn the debugger
3) use strict;
4) use warnings; until you know when you don't want it