Richard Strauss' Der Rosenkavalier is an opera about the passage of time — what it means to grow older, what we lose and what we gain as the years pass, and how we know when it's time to let go of the people that we love. Mezzo-soprano Elīna Garanča knows all about letting go, because after singing the role of Octavian for 17 years, she is giving her final performance as the passionate count this week. But Garanča has no regrets. She's learned to appreciate her life by accepting, and even enjoying, the passage of time.