Which is related to how studios drops additional fastpass inventory. The Fastpasses are available within an hour or 2. But at the time of the window they are booked out.
Which window are you referring to? At the 30 day window, both have been easy to get since they changed the tiers in the summer. And can be picked up easily for any day from tomorrow through next week, month right now.
Have a look at this page from Touring Plans. It will completely refute your assertion it has to do with same day drops. You can change the date and it shows you what is available. This is tomorrow’s availability for DHS. ToT and RnR have availability throughout the day. That is not due to FP drops.
Disney's Hollywood Studios | Disney World | Touring Plans | Crowd Calendar | Wait Times | Park Hours | Attractions | Dining
The definitive guide to Hollywood Studios at Walt Disney World, including FastPass Plus, Toy Story Mania, Star Tours, Tower of Terror, Fantasmic, Disney Junior Live on Stage and more.