The closure was for 10 days full stop. I can't think of a reason to do that in response to an active threat.

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.