I'm not too sure about that because there would be no need to limit the start-time of the kiosks.
The reason is that guests standing 6 feet away from those kiosks could be on-line with their phones booking and re-booking their little hearts out.
Any guest who owns valid Magic Your Way tickets (or AP's) can choose to book FP+:
A. up to 30 days in advance.
B. 30 hours in advance.
C. 3 hours in advance.
D. 30 minutes in advance.
E. 3 minutes in advance.
The point of my arbitrary and somewhat frivolous list above is to ask...
Which of those booking times would offer the better chance of finding more of the popular attractions and times?
So, booking in advance, and the earlier the better, can net guests greater options.
(Yes, I know that WDW Resort guests can book up to 60 days in advance, but that doesn't start with a "3." )