You will need an add-in to do so. Check out the free OfficeOne AutoDateTime
add-in which allows you to insert current date time and update it
automatically: http://officeone.mvps.org/autodatetime/autodatetime.html

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Shawn Toh (tohlz)
Microsoft MVP PowerPoint
Site Updated: April 30, 2007
New PowerPoint Games - Pixels Neon
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> I have created a presentation that continuously runs as a screenshow for
> people to be advised of the buildings and companies security & safety
> regulations. I would like to have the date and time displayed in the
> presentation and have it updated without interrupting the continuous
> screenshow.