Cron was set back to every 12 hours. This is not the best way, to open/close polls automatically. Maybe you will rewrite your plugin not to check the open or close poll date in the database, rather make for each open / close date an own cron entry like wordpress does for each planned post in the future?
Furthermore it is maybe a good idea, to let the user decide, how often the cron checks (hourly, twicedaily, and so on).
Debug is on for tomorrow, when the poll closes.
