UCP 600 Article 14(b), providing rules for the period of the examination of documents, is a radical reorganization of UCP Article 13(b). The provision changes the period of time to a maximum of five banking days instead of reasonable time. One of the critical problems giving rise to the difficulty in interpretation and application is the question of fact that there may be two possible conflicting options in determining the time of checking documents presented. The one doctrine is fixed time(safe harbor) standard, and the other is hidden reasonableness standard. This study analyzes which option should be adopted for the optimal application standard by welfare effect methodology using consumer surplus approach and suggests that safe harbor standard should be optimal solution to the determination of period of examination of documents presented in letter of credit regime.