how do i make a flash frame in iMovie

I'm making a 30 second promo for an event, and I want it to contain a series of really, really short images -- almost a series of flash frames. These are still images that I imported. What is the shortest interval I can make the image stay on the screen? And how do I shorten them?

Second, I have an images that pans from bottom to top, but there is no delay at the beginning nor at the end. I want it to begin on a still then slowly start to pan up, and at the top to end on a still. How do I create these stills?

Thanks,

Hal