When I lived in Michigan, and in Texas, people would generally give distance estimates according to the number of miles the destination, as it "It's about a hundred miles from here." When I moved to California, distance was measure in time, as in "It's about an hour and a half away," which is what they do in Maine too.
I have heard it determined both ways, too. I think that when there are not a lot of people, and you can just get on a good road and drive, then people usually just tell you how many miles away it is to get somewhere. When I lived in the Seattle area, sometimes it could take a disproportionately long time to get somewhere , just because it was on a road with a lot of traffic; so then we tended to describe it as a "20 minute drive" instead of saying it was about 5 miles away. Also, when you are driving in a city, as opposed from one town to another, it is easier to just say how long it takes to get to Walmart or whatever the person is asking. If you are driving from one town to another, there is a highway sign that says it is 20 miles away, so we know exactly how many miles it is, where we often don't really know that about a place that is just across town.
I never realized it but I measure distance in time. I always ask how long will it take me to get there. Miles does not mean anything to me. Only time I want to know about miles is when I purchase a car, how many miles to a gallon of gas will the car get. North and South, East and West, also have not meaning to me. It is left or right, when I give or get directions.
That is something that I really never thought about. As I reflect on it I guess I have been a "time" person, probably because most of my trips were long distance. Even now when I don't drive (people here drive on the other side of the road then the States,and I have a fear that I may go into the opposing traffic if I see an accident ahead) I will say a two hour flight or 5 hours by bus, etc.
This is a little off-topic, but I heard a saying one time that really stuck with me, and I found it interesting. "The difference between the British and the Americans is the American's think 100 years is a long time and the Brits think that 100 miles is a long distance."