"Possibly, possibly," said Beauchamp immediately; "but every simpleton would not be able to understand your heroism, and sooner or later you will find yourself compelled to explain it to them more energetically than would be convenient to your bodily health and the duration of your life.
There are no more uses of "duration" in the book.
Show samples from other sources
I take zinc tablets to help shorten the duration of a cold.
More frequent and longer duration exercise is associated with better health.