Slide transitions in PowerPoint have a fixed, default duration. While some slide transition effects such as Cut take a fraction of a second to take place, other effects like Reveal can take more than 3 seconds to occur. Now these are the default times for the effects — you are not limited to using only the available time spans since you can always increase or decrease the slide transition duration as you deem fit.
Learn how you can change the Slide Transition Duration in PowerPoint 2011 for Mac.

