"Uhm but don't forget Pluto is 40 AU from the SUN - not Earth, so depending on what time of year it is (be it Earth or Pluto, which has a much much much longer year!) it will be 1 more or less AU "

8 minutes 20 seconds travel time... Pretty much negligible when you're talking about Pluto's orbit... You have a variation between 51.5 AU (7 hours 8.4 minutes) assuming opposition at maximum orbit and adding an extra AU to allow for avoiding the Sun; and 28 AU (3 hours 52.8) minutes) at closest approach.