I think the point was to get headlines and attention, as someone else said it sounds like the FAA is frustrated that the DoD isn't cooperating, and this seems like a possible attempt to make this frustration public to pressure DoD into playing more nicely.
This is OpSec 101. Making the public closure too "tight" around the operational timeline could (negligently) leak operational details. You can always cancel a closure later.
The answer is "long enough to avoid giving away operational details," not some robotically applied constant multiplier like 10x.
We also don't know whether they expected this to take 1 day or more. Just because it worked out quickly doesn't mean that's the "worst case" operational timeline.