We've been to Disney three times for 4th of July week, including last summer (2004). We've never had a problem getting into Epcot in the evening.
For July 4, 1998, we went to Magic Kingdom in the morning of 4th of July, then took our nap/swim break, and went to Epcot for the evening festivities. For July 4, 2000, we went to Epcot in the morning, nap/swim break, and back to Epcot for the Fireworks - which were absolutely wonderful!!! For July 4, 2004, again we spent the morning at Epcot, nap/swim break, and then went back to Epcot around 5:00 pm.
No problems at all!!! The fireworks show is fantastic!!!!!
Enjoy your trip!!!
We are going to take advantage of EMH at Epcot on July 4...and then stay all day until the evening festivities! It's going to be a L-O-N-G day! But I heard that it's not as busy at MK on July 4...and since it's EMH at Epcot, I don't want to come later and possibly not get in due to crowds.
Maybe we will get a break in before the evening festivities...Thanks, again for the info. 
