Tina,
The current Epcot calendar shows the park open until 10 pm that evening. I am not sure where you would have heard otherwise, but write us back and we can investigate further.
The one thing I can think of is that the park is in the midst of the
Epcot International Food and Wine Festival at that time, and there might be plans for something special that evening?
There is a Party for the Senses event that evening. This is an extra ticket event, so your regular park ticket would not get you into that experience. Typically that ends at 10 pm, so that is probably not what you might have heard about.
There is also a RunDisney event tied to this event, but it is in November, so again I don't think that is the case.
So for now I would assume a closing at 10:00pm, but write us back on what you heard and we can investigate more!
Have a magical vacation!