You can put up to 4 images on the screen at the same time since you have 4 tracks. But if you have a title and audio, they would take up 2 tracks leaving you with 1.
You didn't indicate which version of PhotoStory that you have. In 2013, there is an error and the PIP effect is really collages, which is not the same thing.
Place an image on track 1, a different one on track 2, and different ones on tracks 3 and 4, one below the other. Click on the bottom one. Go to Effects in the Media pool (upper right area of the screen), open View & Animation, select Size & Position. You should see the dashed line and corner handles on the image that you selected, in the preview window. Drag a corner to make it smaller. You will then see part of the image on track 3. Click on it in the timeline and drag a corner in a different direction to make it smaller, then you will see part of track 2. Do the same for the other tracks. Size and position them as you wish. You can use the position and size or zoom numbers in the effects dialog (Size/Position) screen to get the same size and to help align your images.
Alternatively, you might want to try out some of the collages, but I can't say that the time will be shortened.
In Movie Edit Pro, you can have up to 99 tracks. For about the same price you get much more flexibility.