My 60 day mark was 03/02/2021. When I logged in at 6:00 am the entire week was available to book. However, even at 6:00 am there was a lot unavailable. I did get most everything we wanted, but I did have to move around a park day to make everything work. I would suggest getting on as soon as possible.
Yes. While people like to call it "+10" for shorthand (and it was +10 about a decade ago), it's actually (and has always been advertised as) + length of stay. You should be able to book through your checkout day.