Only 24 days? Does straight walking=no stopping? Because arriving there would be such a huge journey for a wastelander (larger than any protagonist, even the originals, and they traveled *large* distances) that after going there they are more than likely to stay. I also call B.S. on 15 days from D.C. to Chicago, this country is tons larger than you realize.
I'm just going on Google maps, I wasn't trying to say ' It'll take 15 days PERIOD' and, yes, straight walking does mean no stopping. I'm just factoring sleeping and moving in top condition for a wastelander; most people would take longer. GMaps said 10 days walk, So I estimated an extra 5 days because of sleeping,resting, eating, etc.. It could take months to even go that far, if you were wandering there; but if it was your intent to go there, it wouldn't take as long because you would have (mostly) planned out your route on your Pip-Boy. I'd say 30 days max for walking with intent to get there. At 4.3 MpH walk (Average Human's speed) it would take 156.5 hours of (non-stop) walking to get there, meaning about double that, since you could get a good 12 hrs done a day, the other 12 for eating, sleeping, etc. if you stop to eat. That comes out to about 13 days, so, maybe 20 days since paths & roads aren't great.
And 24 days for NV to Chicago; That DOESN'T factor in trekking through the Rockys, eating, sleeping, etc. Using the same equation as before, STILL not counting rocky trek, it would be about (1789 mi/4.6 Mph=416 * 2=832/24=34.67 Days) 34.7 days; so a better estimate would be 70-ish days.
Correct me if I messed up on the math.