I don't understand, there is literally no reason to close it early. It doesn't make for less work or speed up the process of getting the draft started.
I understand why some of the other polls ended early, but this seems to be a different case. I can't think of any downside to leaving it open until signups are closed. Maybe I am missing something, if so please let me know.
On the other hand, there is a clear potential downside to closing it early, which is that some of the late sign ups won't get an opportunity to vote.
EDIT: It is unlikely, but 5 more GMs could sign up and all vote the same way, that would give a clear winner.