It is hard to give an accurate answer because we don't know where in Sussex Norland is situated. As you can see on the map posted by Myretta, Sussex is a long thin county stretching about 70 miles east to west. Even today there are few main roads here which run east to west – the main routes radiate from London, and I think that was also the case in JA's time. We also have to remember that roads were pretty primitive then, so main routes would probably be preferred even if using them added to the distance travelled. I imagine that they would have travelled post, using their own carriage and hiring fresh horses every 10 – 15 miles.

So, a very rough calculation:
Assuming that Norland is somewhere in the middle of Sussex, the distance to Midhurst or Chichester on the western edge of the county is about 30 miles. From Chichester to Exeter is roughly 150 miles, giving a total journey of 180 miles.

A reasonable travelling speed for a carriage would be around seven or eight miles per hour, so they would be on the road for perhaps 24 hours or so, maybe more. I don't suppose that four gently bred ladies would be driving hell-for-leather, but would stop from time to time to eat and refresh themselves, as well as overnight stops.