Hi,
There is no option to limit rating to a time period. But, if you have your own code implementing the poll, and use the function to render rating block, you can change function parameters to disable the rating if the poll is closed. I don’t know how you have implemented this, but function for rating block allows you to pass ‘disable_rating’ value to the method list of arguments to disable the rating.
Check out the documentation for the functions and arguments to use.
Milan