How many hours would it take to walk 11 miles?
On a flat surface, assuming no breaks or stopping, in moderate weather (i.e. not blazing hot or freezing cold), I would say about 3.5 hours.
11 miles is a long way to go on foot, particularly for those people who are not accustomed to going that distance.
For an average person, even if they can comfortably walk one, two or three miles, by the end of 11 miles, I can pretty guarantee their feet will be aching during those last few miles. As such, their enthusiasm and walking speed will be greatly reduced toward the end. Quite possibly, they could be thinking, "Why did I do such a stupid thing?" Ask me how I know all these things.
All those things considered, I think a three mile per hour average seems reasonable for most people.
Qualifications: I've walked 11 miles. It wasn't fun.