Great advice on laundry days.
My copilot, AKA loving wife, gets on phone about two hours before we want to stop or an hour before campground offices close (whichever is earlier) to find a spot for the night in transit. We prefer reservations for the NP.
You need much more time at YNP so plan accordingly. Do you hike? If so, maybe more at GCNP but if you just want to do vistas, just do a couple days and save the time for YNP. I love both so don't get me wrong but I have never seen anything like Yellowstone/Grand Teton for geological diversity and wildlife in one area. And, it's HUGE so just getting around takes hours.
we visited Grand Canyon in winter which was great. Yellowstone in summer so we dealt with crowds more. However, we were there the week of 4th of July and it was doable because we get up early and get to our designated section of the park for the day before most have left their campsite. We bring picnic supplies and find a great view to lunch and get back to campground at dusk again with traffic mostly died down unless there is a bear or something near the road. We prepared easy meals for dinner. We enjoy the campsite for local camping. When I travel to YNP, I want to see the park.
EDIT: search for the many great Yellowstone threads. And bison cause the biggest delays - because they walk down the middle of the road!
