A total of four thousand people participated in a new fitness program. In order to evaluate the effectiveness of the program, the organizers sampled 50 individuals who had completed the program. These individuals were tested by measuring how long it took them to run a kilometer. The average time for these 50 individuals was 6.3 minutes with a standard deviation of 0.6 minutes. Estimate the mean time for the entire population at the 95% and 99% confidence level.