Jump travel time?

Hey all, <br /><br />Something that I have been trying to understand is how long it takes a ship to travel from A to B in the frontier. I get the whole &quot;half the time accelerating, half decelerating&quot; bit from the canon rules. In numerous places, I hear people refer to some ship, usually smaller/faster that can get from A to B faster than another. Maybe I'm dense, but don't all ships take 7 days on a 7 day jump route? Why does it matter if the ship has Ion engines or Atomic when it comes to jumping?