$dbh = DBI->connect("DBI:mysql:db_name:db_host:3306;mysql_connect_timeout=5","username","password");

##</code><code>##


eval {
   local $SIG{ALRM} = sub { die "connect timeout\n" };
   alarm 5;
   $dbHandle = DBI->connect("DBI:mysql:db_name:db_host:3306","username","password") or die $DBI::errstr;
   alarm 0;
};

if ($@) {
   # Timed out
   die unless $@ eq "connect timeout\n";
}