Another (very minor) stylistic point: you can use sprintf to good effect and avoid having to set up a temporary array.

use strict;

my $timediff=0; # set it to whatever

# just get the month
my $month = (localtime(time + ($timediff * 3600)))[4];

# move 0..11 month range into line with human convention
$month  = sprintf("%02d", ++$month);

print ("$month\n");
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Not to worry though, if you're comfortable with your method (TIMTOWTDI, after all).

Tim

Update: simplified to better make the point.