Now a day's Genetic Algorithms (GAs) become a rapidly growing field of computer science. In a Genetic Algorithms (GAs) have many fields to consider for development and have a lot of properties that makes it a good choice when one needs to solve very complicated problems. The performance of genetic algorithms is varied for different parameters that are used. So optimization of a problem by using Genetic algorithms (GAs) is one of the most popular research fields. One of the reasons for this is because of the complicated relation between the parameters and factors such as the complexity of the problem. From the various parameters if we take time constraints as a parameter then what happen, this is our key point for this work. One of the most important parameters is population size and we have found by testing a well known set of optimization benchmark problems that the optimal population size is not the same when time constraints were involved.