What I've learned from my experience at DCA/DL and WDW: the parks will
always be somewhat busy in that Disney is good at keeping their resorts full year round with promotions, special events, etc. What really makes the difference in crowd levels is how many locals and annual passholders are showing up. And during any day at the park, families with children tend to arrive later (gotta get the kids up, eat breakfast, park, get through security lines, etc.) and leave earlier (after the parades/fireworks, etc.), so the busiest times and longest lines will be between 11am - 8pm with it probably being worst Noon - 5pm. Sure enough, that was the case during our one day trip on Saturday, 11/5!
No wonder the Disney planning experts will suggest taking the afternoon off for a rest break if you can afford it. You miss the worst crowds, get some relaxation back at the hotel, give the kids a nap or a swim, etc. Then you come back late afternoon or early evening when the crowds are starting to thin out. I WISH we could do this, but in reality, at both DCA/DL and WDW we needed to maximize our time at each of the parks, so my overall plan involved:
Get to the turnstile well before rope drop
Go hard and fast in the cool morning hours, utilizing an efficient FP strategy
From Noon-5pm when it's the hottest and most busy, see the indoor shows and do the rides where there is an indoor queue and/or lower wait times, or do rides that we've pulled a FP for already
In the evening, get back to the rides and if we still have the energy, take advantage of the last 2 hours before park closing as many people have already left the park
If there's one takeaway from all of this, I would summarize it down to this: No matter what day of the year it is,
mornings (first 2 hours) at the non-EMH park are GOLDEN. (Small disclaimer: the earlier the park opens, the more golden it will be. 8am openings are best!)