what ever you set the gap to will be the load time. the gap is the frame delay, how long it takes to load the frame. that frame delay applies to initial load as well. If you want to display the images instantly, use a low gap value like 1.
the show_img_gap is the time between loading a new frame.
first the gap occurs to load the frame. then the show_img_gap occurs to pause before firing the gap again to load the new frame.