Insert all your png files. Select the top image. In the left panel select display/on move the play-head to the right. Select display off. Keep the play-head at the same place. copy the 2 key-frames for the first image (on and off). Select the next image and do ctrl-v. This will copy the on/off frames for the second image and move the play-head. select the next image and do ctrl-v again. Do the same until all images have on/off. This should complete the animation. See second screen-shot where all the key-frames are shown.
Hopet this makes sense.
