use Time::Local;

sub String2Time {
 $_[0] =~ /^(\d{4})\-(\d{2})\-(\d{2}) (\d{2})\:(\d{2})\:(\d{2})/ or die "Invalid format: $_[0]";
 return timelocal($6,$5,$4,$3,($2 - 1),($1 - 1900));
}

my $t1 = "2009-04-12 23:59:55 PM";
my $t2 = "2009-03-30 00:00:02 PM";

print &String2Time($t1) - &String2Time($t2);