Keynote transition delay time for each slide
In the Animate inspector tab you will find all the settings to easily change transition timing. You can do so for each slide or for the entire slideshow. In the movie inspector you can view the movie length then change your slide transition accordingly. 
I encourage you to explore the user interface. Create a new slideshow just to play with. Then start clicking buttons and menu items. See what stuff does. Just like driving a new car, new software can take a little getting used to but in the long run, a little time invested will pay off. Cheers.