Without seeing how the animations are setup it's hard to tell but a work-around would be to insert a plain shape with no fill colour and no outline (so it's invisible), position it off the slide area and just put a small animation on it for however long you want the slide to remain open and then when you run the animation the last visible animation will run, the invisible one will then run and keep the slide open that little bit longer that you want and then it will move to the next slide.