My 60 day window was this past Wednesday but I was able to book everything for all 5 park days last weekend with this method. It took a lot of time and effort but it was worth it to me to be able to get everything I wanted, and at the times I wanted them.
I was even able to modify the times on my selections before Wednesday. I had a few I wanted to adjust by 5 or 10 minutes. It's more or less the same process. You will usually get an error message when you try to change the time. You just have to keep trying, backing in and out of the app, until it accepts it.