Stretch a Composition?

Hey Guru's, 

    I'll confess to being a bit of a noob, so be gentle.  I created an animated slide show, following a guide on YouTube (no surprise).  It's the one where the photos appear to be dropped onto a picnic table, one at a time, although I changed the background layer to the image of a sandy beach.  Also, at the end of the sequence, I added additional animation to make it appear that the stack of images blows away, aided by a sound effect of wind. 
   It came out nice looking, but once I was finished, watching it in real time, my thought was that each image didn't stay on screen long enough.  After the animated drop, only about an average of 4 sec's per image, which isn't even the default length for a still image in a sequence.  
    What I would like to be able to do, is just to stretch the entire composition, where all animations are just extended proportionally.  So, if I exteded the total length of the comp by 25%, for example, each photo timing would be extended from 4 seconds, out to 5 seconds.  
     Is there a way I can acomplish this, without having to go into each layer, and rework the animation timing?  

    Thanks for your help and guidance.  

     Cheers,   

     Jeff Mulliken