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In this paper we study energy detection for primary user signals in the case of distributed Cognitive Radio (CR) networks. We concentrate on the effects of interference caused by other CR users due to timing misalignments and propose a novel mathematical model for calculating the effects of interfering nodes on energy detection and derive closed-form solutions for the probabilities of detection and false alarm. We verify our model by simulations and show that the impact of interference is severe in the presence of timing errors in distributed CR networks. To the best of authors' knowledge, the problem of inaccurate timing has not been investigated before. However, as we show in this paper, without interference cancellation or precise synchronization, timing errors will degrade sensing performance heavily in decentralized secondary networks and the throughput of CR networks will be significantly lower as well. The results obtained in this work can be used to guide the design and performance analysis of energy-based detection in distributed CR networks when accurate time synchronization is not available.