The stories for last year's SS are on the SS site, y'know. You could peek at them and see the length!
(Which seems to run from "a couple of pages" to "quite long" so I dunno that there really is even a trend.)
ETA: And I have a story idea now. A beginning-to-end, know-how-many-scenes, know-what-the-resolution-is-and-how-to-g