They're going to have to work really fast.
If those are the dates, imagine how fast they will have to work. I know they'll clean everything in there really well. That alone could take months. Also, has anyone built something big, like a recording studio? I imagine that there is a ton of fiber, DMX cabling, electrical, analog audio, etc. Not to mention the track system. Even if you wanted to, you couldn't just throw a ton of people at the job. There is only so much room in there not taken up by objects. Extreme coordination will be necessary, as dependencies for systems will make things interesting. I'd love to see their PERT diagram for that job. Imagine the project ,4 months to update everything that has needed it since the last major rehab.
* Track maintenence.
* Lighting and show elements.
* costume and scene object cleaning and restoration.
* General building maintenence.
* Testing, testing testing.
* Training and user testing.
Now, as we've all done projects of our own small and large, you know it doesn't always go as planned. I would wait until closer to November to predict a real date. If they have any point where a dependency or entire production must wait, the project would see some delay.