Add ability to edit the slideshow text files to add custom delays that overrides the value present in the dialogue. Add code to look for a special delimiter after the filename that would otherwise be invalid in a filename. If it is present and a number is present after the delimiter use this as the delay, otherwise use the default. Something like:
c:\mypictures\picture1.jpg::10
c:\mypictures\picture2.jpg::5
c:\mypictures\picture1.jpg::10
c:\mypictures\picture2.jpg::5