More spectrum opportunity utilization and less interference to primary users (PUs) are two conventional desired objectives of spectrum sensing design. In this paper, we investigate the tradeoff of the two metrics for energy detector through the optimization of the weighted sum of them by joint sensing duration and sensing threshold selection. The problem is proved to be in the form of biconcave optimization problem (BOP). And a joint optimization scheme based on the commonly used alternative convex search algorithm for BOPs is proposed. While it is easy to add metric thresholds to the problem and the proposed algorithm without incurring complexity increase, the joint optimization scheme itself does not rely on predefined sensing duration or threshold. Simulation results demonstrate that the joint parameters optimization scheme generate 32.0% and 85.9% preference over single parameter optimization schemes on average, while the spectrum opportunity utilization ratio is high with low interference probability to PUs.