Yes you can. While preparing a Decision the User can either close the Decisions manually or let the system close the Decisions automatically, based on a date/time which has been entered in the section "General" under "Automatically close on".
Once the Date/Time entered under "Automatically close on" is reached, the Decisions will close automatically, even if there are still Participants with pending responses.
Alternatively you can choose to close the Decisions manually, at anytime.
Just do the following:
1) On the section "Decisions" click on the Decision you want to end/close. It's a link and you'll be guided to the next section.
2) The dashboard page will open.
3) On top of the Page next to the Title you find an orange button ""Close decision now"
4 Click on it an a confirmation panel will open "You are about to close this decision. Participants who haven't responded yet won't be able to cast a vote. Are you sure?
5) Please type 'CLOSE' to confirm your final decisions.
Please be aware that this command can't be undone!