You'll be able to do all week when your window opens, so start with your last day and go backwards if you are looking for Anna and Elsa! Everything else you should be fine getting at the 60 day mark.
This demonstration was done on a PC, which I find much easier to do selections on - if anyone wants one on an ipad or phone, please comment or let me know on Facebook and I'll be happy to do so! You log in to make your selections under My Disney Experience, https://disneyworld.disney.go.com/fastpass-plus/
Now select your park and the date you want to choose Fast Passes for. Any dates you are eligible to make selections on will be shaded blue. A check mark will appear if everything is in order.
You will now see a screen with four options for time slots.
The confirmation screen comes up with the times you have just selected confirmed. There is a button under the ride name that says "Modify". Assuming the three options did not come out exactly as you wanted, you will click on "Modify" now.
So that's it! You've now successfully made fast passes for the first day of your trip (or the last, if you start from the end). Continue that process until you have selections made for each day of your trip!
Questions? Comments? Concerns? Hit the comments section below, send me a message, or come on over to Facebook and ask me there! And remember, this is why you want to have a vacation planner! I can help you understand how it works and give you more tips to help you enjoy this system, or I can make the selections for you if you prefer - I'm here to simplify your vacation!