It's run by the Glock Shooting Sports Foundation. Every match has the same format and the same rules (both available on the site). You must join GSSF to shoot a match, and pre-registering is a little cheaper than on-site.
You can show up any time between 0900 and about 1500, either Saturday or Sunday to shoot once you've registered.
If you haven't done any shooting except at a range, try this -- it's a blast.