This paper presents a method to optimize the timeout value of computing jobs. It relies on a model of the job execution time that considers the job management system latency through a random variable. It also takes into ac- count a proportion of outliers to model either reliable clus- ters or production grids characterized by faults causing jobs loss. Job management systems are first studied considering classical distributions. Different behaviors are exhibited, depending on the weight of the tail of the distribution and on the amount of outliers. Experimental results are then shown based on the latency distribution and outlier ratios measured on the EGEE grid infrastructure. Those results show that using the optimal timeout value provided by our method reduces the impact of outliers and leads to a 1.36 speed-up even for reliable systems without outliers.