I suppose you'd have to or you could easily take a week getting there on back roads & stopping to see things. You will most likely still need at least one overnight stop depending on how early you get off etc.
I did the South of France in 18 hours in one leg, but that was 25 years ago & they have cameras on the motorways now, they work out how long it took you from one toll to the next. From that they get your average speed.
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