Is there a way to end voting after a specified period of time?

I don't think this feature exists.

I'm no expert, nor even a user of this module yet - but I'm thinking that it's possible to set a trigger or a rule such that: on [date+time] change permissions on [x node] where authenticated users do not have permission to edit node.

You might have to find a good node permissions manager...again, I'm not expert and could be out to lunch on this.

Good luck

I can confirm that this feature do not exists yet.
Adding to grifcha solution: what about using triggers/rules in combination with content_access?