Cron Expression (Quartz) for a program to run every midnight at 12 am

1 Seconds
2 Minutes
3 Hours
4 Day-of-Month
5 Month
6 Day-of-Week
7 Year (optional field)

So in your case:

0 0 0 * * ?

This will fire at midnight, if you want to fire at noon:

0 0 12 * * ?

Or both:

0 0 0,12 * * ?

A good page if you want to get more complicated: http://www.quartz-scheduler.org/documentation/quartz-2.x/tutorials/tutorial-lesson-06

Have an awesome day!