Minimum Inaccuracy for Traversal-Time
  Using various model clocks it has been shown that the time-of-arrival cannot be measured more accurately than 1/E where E is the kinetic energy of a free particle. However, this result has never been proved. In this paper, we show that a violation of the above limitation for the transit-time, implies a violation of the Heisenberg uncertainty relation. 
J. Oppenheim, B. Reznik, W.G. Unruh