code: func JitterDuration(average, plusMinus time.Duration) (ret time.Duration) {
  	ret = average - plusMinus
  	ret += time.Duration(rand.Int63n(2*int64(plusMinus) + 1))
  	return
  }
docs: // Returns random duration in the range [average-plusMinus,
  // average+plusMinus]. Negative plusMinus will likely panic. Be aware that if
  // plusMinus >= average, you may get a zero or negative Duration. The
  // distribution function is unspecified, in case I find a more appropriate one
  // in the future.