Roasting pork and traveling
That's actually just about perfect, since meat should rest before you slice it. Start the roast at 3. Cook it for 2 hours. Wrap it in aluminum foil. Put it in something to retain heat (a cooler, or even just a box with some towels). Drive 1 hour to your destination. 

The muscle fibers will re-absorb the moisture, making it perfectly juicy. Without resting, it will seem "juicy" when the juices pool on your slicing board, but that's moisture that's lost. The sensation of juiciness is strongest when it has re-absorbed the moisture among the fibers, so it comes out in your mouth when you chew.

Wrapping it in aluminum foil will keep it warm as you go. Heat will equalize throughout the roast. Since it cooks from the outside in, the outermost layers are hottest. Take it just to the very bottom of the cooking range (145°F), or even a little lower, and let the carryover heat from the hotter outer layers finish the cooking. It will arrive perfect for you to slice and eat.

If you're eating any later than, say 6:30, then keep it warm in the oven at 200 or even 180 if your oven will do that. Another hour of warmth will still be perfectly safe, and won't go too far towards moisture loss.