Construction development in Indonesia is being intensively carried out as a characteristic that Indonesia is a developing country. CV. X is a construction company that has a project in the form of ten shophouses with three floors. The projectis planned to start in August 2020 and be completed in December 2021 or for 68 weeks. The change of seasons becomes an obstacle in the work of the project that causes delays. Progress expected by CV. X in 2 months of project work is 8%, but the reality onthe project progress field is only 6%.Therefore, this study aims to optimize existing work time so that the delay can be overcome. The method used in this study is ProgramEvaluation and Review Technique (PERT) with rainfall as the probability.The results of the study found that the project work time can be optimized by 3% and delays can be overcome because the project completion time becomes 66 weeks.The project is still ongoing,so there is still a possibility of error, therefore effective project management must still be considered. Usually in similar studies the probability of time or cost, while in this study use rainfall as the probability.