The mean job inter-arrival time is 0.667 time units and follows an exponential distribution. Processing times at each machine follow a 2-Erlang distribution with a mean of 1 time unit, except for the machines of work centre 1. For these machines, the mean processing time is 2 time units. This leads to a 90% average planned utilization in all machines. Due dates are modelled as a random variable and are determined by the order arrival time plus a discrete uniformly distributed time allowance. The minimum allowance value equals the planned shop flow time for the maximum of 6 operations. The maximum allowance value