Treason happens only during wartime correct?
Time of war. Treason by aiding the enemy can't be committed during peacetime; there must be an actual enemy for the traitor to aid. The requisite enemy designation typically requires a formal declaration of war.
Treason and terrorism differ in that anyone (not just nationals) can commit the crime of terrorism and terrorism doesn't require that the United States be at war. (There are, however, similarities between treason and terrorism-related offenses—for instance, statutes criminalize providing material support to and harboring terrorists, among other actions.)