Optical packets assembly algorithm is analyzed when traffic shapes in an optical resilient packet ring (ORPR) network and a new algorithm is proposed for ORPR network by controlling the time in transmission. The algorithm is based on a hybrid threshold assembly algorithm. It adds a parameter to control the interval between optical packets so that the traffic in each time unit is smoothed. It also ensures the quality of service (QoS) performances of the network and fits for the ORPR network with limited optical buffer. The average assembly time-delay of optical packets is analyzed in detail. By adjusting the interval of packet transmission in the new algorithm, we obtain about the same distribution of assembly time-delay under different traffic loads. The stable packets average assembly time-delay is very important to QoS and fairness of ORPR. Choosing the good timing for packet transmission is one of the keys to ensure the QoS and fairness of the ORPR. Simulation results demonstrate that the new algorithm gives a relatively stable packets average assembly time-delay and dispatching is satisfied in most situations in the ORPR network.