Mitford was a city of ten thousand people only a day and a half down the road, so that was their goal. If they could make it there early, they could trade some goods at the market in town, or to a local shop, and have time to relax and eat before leaving town for the night.
It was safer to be out of the cities to sleep, and that let Thor have a proper rest in his space, instead of some filthy barn somewhere.
The number of farms didn't decline much as they travelled, there was one every quarter kilometre for the entire day. But the quality of the road didn't decline either, it was a well-groomed gravel double track, wide enough for two fully loaded carriages with guards to pass each other.
It made progress much more comfortable, though Thor didn't speed up much, for the sake of everyone in the wagon.