Two Hands wrote:
You don't realize just how big Yellowstone National Park is. You will waste so much time driving to and through the park that you won't have time for even short hikes. Then trying to drive down to the Tetons for a day! Way too much time driving instead of looking. I highly recommend you consider staying in or immediately outside Yellowstone for at least three days then go down to Tetons National Park for a minimum of two days. Staying between the parks to see them both can definitely be done, but not if you want to really experience the parks.
X2
We have stayed at Fishing Bridge in YW park and then moved outside to the West Yellowstone KOA. Next time we'll skip West Yellowstone and stay at Fishing Bridge and Colton Bay. Driving times in the park are longer than you expect, especially with any traffic jams which were hard to avoid NW of Fishing Bridge due to how animal sightings on the road side affect traffic.