900 miles in a day is stretching it, but not entirely out of the question. You can sustain a long distance average speed of about 55-60MPH (counting time for stops) in a Model S 85. It will be slower than you could do in a gas car if you push it. If you don't push it, it won't be any slower, and could even be faster. (Refueling a gas car takes a lot less time, but can't really be done concurrently with other things. If you were going to get coffee or whatever at each charging stop regardless, then you're looking at 5 minutes for gas versus zero for electricity. Accomplishing this with perfection is, of course, a bit of a challenge.)

Note that an hour every 300 miles isn't generally how you'd do it. Charging is faster the closer your battery is to empty, so your best bet is to work in the bottom ~50% of your charge range when possible, and spend ~20 minutes charging at intervals of ~150 miles. You'll note that this is about how far apart Tesla's superchargers are spaced. That, to me, is about the right interval for a quick coffee, bathroom, or stretch break. Your mileage may, of course, vary.

The biggest problem with your particular trip isn't the time for charging, but the general lack of charging infrastructure along the shortest route. If you route through superchargers, the distance is about 300 miles longer due to the need to take I-70 into Kansas to follow the chargers. This should improve with time, and current owners will benefit, but until it does there are some trips that are just not as good with superchargers. But improvements there pay off a lot better than improvements in range beyond 300 miles.