Powerpoint timer

[Gerschwin]

Hi

I'm trying to figure out a way that a timer can be inserted into a Powerpoint presentation that times the whole slideshows length. eg. If I have a presentation with 100 slides I would like to trigger a prompt after 5 minutes no matter what slide I was on.
Not sure if it can be done with master slides?

Anyone any ideas?

Cheers

 

[Gerschwin]

Unfortunately I can't run other apps on the lappy to be used...cheers anyway

 

[Gerschwin]

I'm trying to think of the purpose of timer. If you were displaying the presentation to an audience at the same time, surely the prompt would also be seen by the audience and not just by you?

It's for a short presentation that can't run over - need a prompt say 60 secs before times up so I can quickly finish.....