Agree with the above posts.
For some clarity, you will probably arrive and depart from the same terminal (T5). A very short walk. If you arrive in T6, it is an extra 5 minutes walk (airside).
If you are nervous, just wait for your schedule to change by a minute or so (happens often), then call and ask. Even if DL is not obligated to help you, they might put you on a JFK-LAX flight if it is in their best interest.