Does any of the workers actually work on Saturday nights or do they just sit inside goofing off?

They goof off. But what do you expect from kids making minimum wage

This is the link to contact McDonald's corporate. https://www.mcdonalds.com/us/en-us/contact-us/restaurant-feedback.html

If you have issues with service talk to the manager or contact the owners / corporate about it.

Very slow service at night