By Litte's Law, the arrival rate to the waiting room (l) is equal to the number of customers in the waiting room (L) divided by the amount of time a customer spends in the waiting room (W), ie., l = L/W. If the arrival rate to the post-injection waiting room is less than the throughput of the vaccination stations, then removing (or reducing) the waiting time after an injection is going to improve performance of the system.