Build-up diagram \# of Customers in system (in service + waiting) customer, the customer who arrived the second earliest the second custome The service discipline is first-come-first-served (FCFS). According to the diagram, what is the service time of the first customer in minutes? The following build-up diagram tracks the number of customers for a single-server queueing system (e.g., an ATM machine) from 10:00am to 10:15am on a certain day. The number of customers shown in the chart includes both those in service and waiting in line