public long elapsedTimeMillis() {
    if (stopTime == 0) {
      return System.currentTimeMillis() - startTime;
    } else {
      return stopTime - startTime;
    }
  }
Returns the elapsed time in millis since starting. Value is final once stopped.
geode-core/src/main/java/org/apache/geode/internal/util/StopWatch.java