Changing pics at different rate that the master one

Hey guys I got a quick question …
how can I change pics at different frame that the master movie …
which is a 40 frames

let say that I wanna make a new SWF and I want the transitions between 3 pics or whatever pics I want … at 20 frames … Im loading this into the master movie so when I loaded my transitions it run at 40 frames not at 20 as I speceified in the properities … so can anyone help me on this thanks guys ?

or maybe I was thinking in doing something like for example each 10 seconds change to next pic and so on ? can you do something like that ? maybe with set interval ?
thanks