It did use to be 2 years (the luau at The Polynesian was too) However when they went to a uniform 180 days for everywhere (well apart from Bistro de Paris) it followed suit. I think that was a couple of years ago. It does looks like it may well be 90 days soon. When I booked up, a few years back I ended up in what would be tier 3 seating, and that was with maybe 100 days to go. So people really did book well ahead for it. I was amazed. However I will add our upstairs, at the side seats, where really good.
It's 180 days even if you're not staying on property. If you're on property, though, there's the "180+10," which means you can call on your 180 day mark, but make ressies for that day and up to 10 days after you check in. Not sure if, when it goes to 90, it'll be 90+10.