Just remember that the contest stipulated no 'professional' entries.
Might I suggest... and this has worked well for several of the 24 Hour, 48 Hour and 72 Hour Film Festival/Challenges I have participated in...
Require certain objects and lines be included in the film submissions.
For example, one of the last 48 Hour Film Festival I participated in, The A3F 2009 required a theme: "A Significant Loss", a Line of Dialogue: "This changes everything", and a backpack as the prop where one or more characters had to either open or close a backpack.
This ensures the film is written, shot and edited in the time limit provided or in our case is exclusively intended for the contest.