At one time or another I have driven every mile of the trip as you described in your reply. Like you, I have encountered those who [are unfamiliar with the driving distances in the western US]. I’ve even met folks that cannot discern the difference in scale on a road atlas from switching the pages between Montana and Massachusetts.
I see this regularly with Army inspectors who call me and say that they want to fly into Billings, inspect Army Reserve units in Billings, Butte, Helena, Great Falls, Missoula & Kalispell all in two days and then fly out on the third day. 🙂
Not counting any of the half-day side-trips that you mentioned, Mapquest estimates a driving time of “19 hours, 31 minutes, and a Total Estimated Distance: 1,114 miles”. Regards, – Ed in Montana