You do not absolutely have to, but there is a sigicificant practical issue if you give less than 3 weeks (?). The NYSE does not allow its member firms from voting uninstructed w/o sufficient notice. That means even getting a quarum can be a pain as many retail investors do not vote.
The 13 months is DGCL, but there is basically no penalty and NWBO was late on that as recently as 2 years ago.