code: func DurationMinusBuffer(intv time.Duration, buffer time.Duration, jitter int64) time.Duration {
  	d := intv - buffer
  	if jitter == 0 {
  		d -= RandomStagger(d)
  	} else {
  		d -= RandomStagger(time.Duration(int64(d) / jitter))
  	}
  	return d
  }
docs: // DurationMinusBuffer returns a duration, minus a buffer and jitter
  // subtracted from the duration.  This function is used primarily for
  // servicing Consul TTL Checks in advance of the TTL.