I'm not sure this is correct, you may want to check MesaBoy's link.
I have AP, so it may work differently for a finite ticket, but when I'm not staying onsite and have a 30 day window, it's 30 days for each day. So I can make FPs for May 14 tonight, May 15 tomorrow night, etc....
And when staying onsite, its for the full length of your stay, providing you have the admissions necessary to cover it. So when I stay for 16 days in August with my AP onsite, I can book FPs for all 16 days starting at 60 days from my first night.