Just make sure your script follows the basic "5 Act" method of screen writing. If it is going to be about 30 minutes, you don't want to have a lot of down time. Make sure you develop the characters well enough. Rule of thumb: make a backstory for each main character and incorporate bits of them in the movie's story when trying to build characterization.
My experience:
Film School
Screen writer: 12 years
Director: 10 years
Editor: 8 years
Visual Effects Artist: 5 years
Drector of Photography: 3 years