We ate at Le Cellier on the 4th of July in 2002 and we had to wait about 45 minutes past our PS time. I can't remember what time we had the PS for, nor can I remember what time we finished, but it was before Illuminations, because I remember having an impossible time getting from Canada to the International Gateway, it was extremely crowded.
On an up note, Epcot on a whole was not crowded that day, just at Illuminations time around the lagoon.