Sergeant Knight knew all about Majorca, and so did Orr, because Yossarian had told them often of such sanctuaries as Spain, Switzerland and Sweden where American fliers could be interned for the duration of the war under conditions of utmost ease and luxury merely by flying there.
There are no more uses of "duration" in the book.
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I take zinc tablets to help shorten the duration of a cold.
More frequent and longer duration exercise is associated with better health.