I just went through this with booking my honeymoon.
I secured 2 F seats two days after the calender opened up for the departure. You have to wait 2 days after your intended depature dates to account for the change in time. Two days after my departure dates opened up on the calendar I booked a placeholder return. This secured the outbound availability. Once your Return dates open up on the calendar Call ANA to change the return portion of the flight to the dates you want. There's no charge or fee if you simply change the dates.
Things to note :
I found award space on my placeholder return dates, so my flight was ticketed upon booking and then was re-ticketed when my actual return dates with space available opened up.
You can not change the class of service or any airports without a 3000 mile fee. This also requires you to cancel the entire award and no way to confirm if space will reappear. It becomes a crap shoot if the return portion of your flight will have space available any time close to the return dates you want.