According to the documentation (perldoc Time::Local):

the month is the number of months since January (0..11).
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Therefore, August should be 7, not 8.

I can post all the code if necessary

Just the opposite: you should reduce your code to the smallest number of lines possible to reproduce the problem.

#!/usr/bin/env perl

use warnings;
use strict;
use Time::Local;

timelocal(0,0,0,31,8,2011);

__END__

Day '31' out of range 1..30 at ./923524.pl line 7
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