We always go at this time. Whilst there are queues for some rides on some days, it's not too bad at all. Most rides we walked straight on or with up to 10 minutes waiting, a couple of others were about 30 mins, but with the pre-shows and the interesting queuing areas it wasn't a problem.
You can use Fastpasses to deal with the worst queues e.g. TOT, RnR, TT, Space and Splash Mountains (in my experience), and try to eat earlier or later than normal meal times to avoid the crush.
I have quite low crowd and queue tolerance and we're going back for the 4th time this year, which must say something.
I don't think the Americans are on holiday at this time - the place is full of Brits, though!!
Have a wonderful time!