How do I run a cron job on a Mac?
I think in OS X you should use launchctl for "cron jobs".
But otherwise your task should be easy to do with a cronjob
sudo crontab -e
55 23 * * * wget http://www.math.columbia.edu/algebraic_geometry/stacks-git/book.pdf  

This should run everyday at 23:55

Update

You should specify the output location of WGET with -O /path/to/file