Opportunistic routing has gained much attention in recent years as a means of leveraging the broadcast nature of wireless medium. Most of the previous studies focused only on improving throughput, assuming that Best Effort traffic which is delay insensitive is delivered through opportunistic routing. However, when the delay sensitive traffic is involved, it is necessary to consider both the opportunistic gain and the delay incurred by opportunistic routing at the same time. In this paper, we analyze the relationship between these two factors and through extensive simulations confirm that our analyses are very accurate.