I suppose there's always a chance that they could re-open ahead of schedule, but I'd say it's doubtful. I think that after all these years Disney is pretty good at scheduling maintenance. On the bright side, I have been to Disney during times when some of my favorites were under refurbishment, and we were having so much fun that we hardly noticed.
There have been some rides that open early but in general the rides seem to open on the dates they give. As well, there are times when the rides open after the initial dates given but this seems to be rare.