PowerPoint has tools to record and time your presentation, so you can practice your timing before you're actually in front of an audience.
Rehearse your presentation
Select Slide Show > Rehearse Timings.
Select the Next arrow to go to the next slide. Or click the mouse or press the Right Arrow key.
The number to the right of the Pause icon is the time for the current slide. The time to the right of that is the time for the whole presentation.
Select the Pause icon if you want to pause recording. Select Resume Recording to resume.
When you reach the end of the presentation, select Yes to save the slide timings, or No if you don't want to save them.
Note: You can also press Esc to stop recording and exit the presentation.
View the timings
Select View > Slide Sorter.
See how long you're spending on each slide.