4.105 miles.
I think you guys are reading too much into the "everything must open at once" thing. I think that for softs they will be able to open or close parts of the island as needed as long as for the "Grand Opening", as in when they fling the gates open to the general public, the entire island opens at one time. This was in the contract to keep Universal from opening Hogsmeade and then 6-12 months later opening Forbidden Journey.