2 days in Yellowstone is barely enough time to see the highlights, expect it to take 2 full days just to drive the main figure 8 loop at Yellowstone, briefly stopping at the major attractions only, and skipping some of the secondary thermal features, waterfalls, visitors centers, etc. Yellowstone is BIG, and the loop road alone is 142 miles with 45 mph speed limit, which drops to 0 mph when wildlife is present. It would be easy to fill up a week in just NW Wyoming, and not come close to seeing all the major attractions that are within 100 yards of the highway. We spent 3 nights and 4.5 days in Yellowstone in the summer of 2017 just before the big solar eclipse and were barely able to hit the highlights.