How can I change the voting period?
Topic on Extension talk:SecurePoll
On Special:SecurePoll there's an edit button for each poll. That'll allow you change the period (if voting has not ended)
The vote wasn't closed, but I wasn't able to edit the voting period.
I should've added 'if the voting hasn't started' too. Yes, this intentional limitation. I see you've already opened T344300, so linking it here for reference.