Disney has officially said that the closure is from Jan 4th for 6 months, with no specific re-opening date. ANY and ALL dates you see posted on ALL websites are simply place holders. Don't base any trip on the reopening date for the attraction.
Most websites use automated systems that can only function on actual dates, so with a lack of specific data, they have to toss in an end date, so that they closure its self will show in their sites database. June 1st is a handy generic date to use. I am certain that as it gets closer they will adjust. Having said that on long, major projects, Disney almost NEVER gives an opening date. Skipper Canteen is the latest example, but the Frozen in Norway is only a few months out, and they are still saying spring. I am sure that they will say "It will open as soon as it is show ready"