30 minutes is enough to go landside T4 to T3. There are no tunnels connecting T4 to T3 and there is no way to walk between them airside. There are tunnels connecting T4-T5-T6-T7 airside, however those tunnels were closed several years ago (after repeated need to evacuate all of the terminals after a security intrusion at any of them). Recently some of the tunnels are open, sometimes, but they don't help you to get to T3 from T4. It is literally a 5 minute walk from T4 to T3, and another 5 minutes to get out of T4. That leaves you 50 minutes to get through security at T3 -- I've never seen it take over 5 minutes, unlike at some of the other terminals, such as T1 (Southwest) where it can take an hour. So you should be in good shape for the connection, just don't dawdle and go straight to T3.