Wow, all great answers and a big help. I can hardly wait to get started. Thanks responsive monks!

Update:
It worked as shown below. Good stuff and sorely missing from the literature. Maybe this would make a good Q&A (now an unapproved question, under subroutines).

#!/usr/bin/perl

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

use strict;
use CGI::Carp qw(fatalsToBrowser);
use Validate;

my $the_time = "12:23 pm";

Validate::val_time($the_time);

$the_time = $Validate::val;  

if ($the_time) { print "$the_time\n" } else { print "error\n" }
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And the module:

package Validate; # use package to declare a module

our $val;

sub val_time {
    $val = shift;
    $val = ($val =~ /^(\d{2}):(\d{2}) (am|pm)$/) ? "$1:$2 $3" : 1;
    return $val;   #worked with and without this line
}

1;
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Thanks!