Wednesday, April 15, 2015
This day is covered in these episodes:
This date is a guess, the events could have happened on any day between April 2 and May 18.
Kinoshita finishes the storyboards for episode 1 of Third Aerial Girls Squad. Meetings start almost immediately after.
All meetings up to the meeting about the soundtrack happening on the same day is unlikely, but none of the characters change their outfits over this entire ~12 minute long sequence of scenes.