Assume a really fast rocket is traveling from galaxy A to galaxy B. Due to relativistic length contraction, the distance between the galaxies is less as seen by the rocket than it is for a stationary observer in either galaxy. So the travel time from the perspective of the rocket (the "proper time" of the rocket) is less than the travel time measured by a stationary observer. And when you work out the math, the rocket's proper time approaches zero in the limit as the speed of the rocket approaches light speed.