Yes with the PowerPoint Add-In it is possible to add a countdown clock to your polls.
- Select the slide you would like to add a countdown clock to
- Click on the Display Options button from the ribbon
- In the display options menu you can enable or disable a countdown clock and choose how long you wish the timer to last for
By default the timer will be added to the bottom right of your slide but you can easily click and drag it to re-position it anywhere you like on the slide.
The countdown clock does not automatically close the poll. When the clock reaches zero you can still wait to allow time for a few late responses from your participants and then you must manually advance the slide to close the poll.
The countdown timer will only appear within the PowerPoint presentation. No indication of the timer will appear on the devices of the participants.