Your project looks very interesting.
I've been recently dabbling with Google Scripts to do some cool stuff for my own needs.
With all these in mind, I can help you achieve what you need.
Using Google Scripts it would be possible for me to create a spreadsheet with a Gantt Chart given a set of parameters.
Based on what I understand from your requirements, these parameters would be:
1. Task List (this would include all the details of each task, eg. Length, Description, etc.)
2. Audition date
Also with Google Scripts, it would be possible to generate a PDF file that can be emailed to whoever is auditioning.