Holy shit.
From this it's 1277 miles.
http://www.travelmath.com/drive-distance/from/Tucson,+AZ/to/Springfield,+MO
That works out to approximately 64 miles per day for 20 days, 80 miles per day for 16 days. Yeah, good luck with all that DUmmie. Even if you walk 20, and ten, add 2, whatever that means, you're looking at 40 miles per day, walking. Uh huh. Can't wait to see this headline.
The average person's walking speed is between two and three miles an hour. Top walking speed is about 5 MPH.
So - let's give the primitives the benefit of the doubt, and assume they are championship walkers, and they can hit and maintain 5MPH indefinitely.
The trip will take them 255 hours and 20ish minutes. In other words, it will take them better than 10 1/2 days to make the trek, if they move nonstop & at top human walking speed.
BTW, the average person walks half of that - 2.5 MPH - So, at 24 hours of walking a day nonstop at 2.5MPH, their 20 day journey will take them about 22 days.