This study aims to determine delivery time of a set of customer orders in a repetitive make-to-order (MTO) manufacturing company that utilizes recycled waste products as raw materials. A simulation approach and flow-shop dispatching rules are applied to find minimum total flow time or makespan taking materials supply uncertainties into account which is then used to determine the delivery time of each order. As an industrial case study we consider a small medium repetitive MTO company that produces multiple products from plastic waste. The result of the study shows that in a flow-shop manufacturing system with probabilistic arrival time and quantity of materials shortest processing time rule does not always result in minimum makespan.