Axis Sally/Mildred Gillars was held for over a year AFTER WWII before she was charged (and eventually put to trial where she was sentenced for treason). And she was just an on air propagandist for the Nazis, not a active combantant.
Did we try many prisoners during the war or did we wait until afterwards?
Spies, saboteurs, and out of uniform were tried and sentenced immediately. Legal combatants, after the war, under new legal proceedings.