—Many disturbances can occur during the execution of a manufacturing scheduling process. To cope with this drawback , flexible solutions are proposed based on the offline and the online phase of the schedule. Groups of permutable operations is one of the most studied flexible scheduling methods bringing flexibility as well as quality to a schedule. The online phase of this method is based on a human-machine system allowing to choose in real-time one schedule from a set of schedules that fits best the real state of the system. In this paper, we propose and evaluate a new criterion called the best-case in order to be used in real-time during the online phase of the groups of permutable operations. This criterion offers an optimal or near-optimal solution from a set of solutions. The usefulness of this criterion is showed using a comparative review with two other criteria on a benchmark instances using the maximum tardiness objective.