We consider the problem of a packet multiplexor that receives packets from multiple input flows, then forwards them to a single output channel. The multiplexor ensures a predefined forwarding rate for each flow. This is achieved as follows. The multiplexor assigns a timestamp to each received packet. When the channel becomes idle, the multiplexor forwards the packet with the smallest timestamp. In this paper, we show that the multiplexor efficiency can be improved without sacrificing packet delay by maintaining one timestamp per flow rather than one timestamp per packet. We show that this approach improves the computational efficiency of two known multiplexing methods, namely, virtual clock and self-clock.