Open PowerPoint and go to the slide where you want the timer
Click the Insert tab
Select Text Box, then click on the slide
Type the timer text, such as 00:00
Go to the Insert tab
Click Add-ins or Get Add-ins
Search for a timer add-in and install it
Insert the timer add-in onto the slide
Adjust the timer size and position
If using a video or GIF timer, go to Insert
Click Video or Pictures and add the timer file
Resize and place it on the slide
If using animations, select the timer text
Go to the Animations tab
Add animation effects as needed
Set the timing in the Animation Pane
Save the presentation
Start Slide Show mode to test the timer