I don't know about Sunday being a common deadline. It sounds odd and very unlikely to me.
Someone upthread noted that memo #4 is dated August 18, 1973, which was a Saturday (I double checked and they were correct). That Saturday memo is filled with references to other entities and "today" as if a group and people were all confabbing on that exact day. Another unlikely and odd occurrence.
"Another unlikely and odd occurrence. "
Come on guys, this is the National Guard! Except for the fulltime admin staff, the only time the entire chain of command was on hand and the forces were drilling would be the WEEKEND, e.g. Saturday and Sunday.
Unless it was annual training or some other time.
Sa and/or Su make actually MORE sense for a Guard situation than a weekday would have . . .