^I have some quasi, semi-relevant, grain of salt experience. Last year, I visited the park on Monday, July 5th and Wednesday July 7th. I assume most people got Monday off for the 4th. Quick Queue unlimited sold out Monday. Despite that, I was able to ride every ride in the park that I wanted to with some rerides using only standby lines (Griffon was down for my visits and Pantheon had yet to open). Lines and crowds were about the same levels on Wednesday.
I would likely recommend buying QQ in advance.