In this paper, we investigate the usage of millimeter- wave (mmWave) band and sub-6GHz band with respect to total transmission time as a performance metric. For mmWave communication, multi-hop relaying is considered, and it is able to operate as half-duplex of full-duplex mode. By consider simple system model, but not disregard its inherent characteristics of each band, we analytically investigate the trade-off between each band, and derive the conditions for each best-performing regime. In the end, we observe the trade-off with respect to various system parameters and our analysis is well matched with the simulation results.