Also, in this simulation are the customers arriving in equally spaced intervals or is random arrival time within the bounds assumed?

Aren't they arriving slightly slower than can be served, according to these numbers:

If one customer takes 10 minutes to serve, you can serve 6 customers in an hour

and you get 5.8 customers every hour, which is less than 6

So you serve 6 customers, meaning you have a leftover capacity of 0.2 per hour or 1 extra customer every 5 hours

Maybe the numbers are switched over or I am misunderstanding something

Edit: nevermind, read the link in the thread and realised I treated the average as the actual serving time and I'm guessing that's what makes it non intuitive. I'm still not entirely clear on how it works.

They're arriving slower than they can be processed. So the line shrinks slowly it there's a line.