There is a thread on it:
Leading Reservations for dining? - Walt Disney World - TouringPlans Discussion Forums
That explains it with a link to how to do it. But in a nutshell you would book a reservation for 10 days prior to your checkin so yes in this case June 17 but you would book it thru the last day you want to make any Dining or Tour reservations (etc. cabanas is another one). Then each day you are 70 days out from what you want to book you can book it. So if you wanted to Book WAT for June 27 you could book that 70 days prior instead of 60. Because yes the 60+10 is exactly how you described. Once you get to 60 days from your actual checkin date you can cancel the leading reservation and get your deposit back which is equivalent to one night’s stay regardless if it’s for 1 night or 15 nights. So you’re temporarily out the same amount of money either way.