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


while (<DATA>) {
    if (/FIND/) {
        my $now = time;
        my ($month, $day, $year, $hours, $minutes, $seconds, $AMPM) = split /\/| |:/;
        $hours += 12 if $AMPM eq 'PM';
        my $time = timegm($seconds, $minutes, $hours, $day, $month-1, $year-1900);
        print "within 30 mins" if $now - $time < 30*60;
    }
}

__DATA__
7/21/2009 5:47:29 PM:> DATA 
7/21/2009 5:48:49 PM:> DATA1 
7/21/2009 5:49:20 PM:> FIND 
7/28/2009 9:49:20 AM:> FIND 
7/21/2009 5:50:39 PM:> DATA3 
7/21/2009 5:51:29 PM:> DATA4 
7/21/2009 5:52:59 PM:> DATA5 
7/21/2009 5:53:19 PM:> DATA6