Remote handling operations during a shutdown of a fusion plant like JET or ITER are executed according to formally described and validated procedures. Unexpected events during the execution of the procedure may require rescheduling, suspending the execution of the current procedure to pick it up later. In this paper, we investigate whether the introduction of a certain amount of slack influences the robustness of the overall shutdown schedule. First we introduce a classification for different types of anomalies that may occur during execution of operations. We introduce a set of metrics to measure the robustness of a remote maintenance schedule against various types of disruption. We then simulate the occurrence of disruptions in a set of procedures, and evaluate the effect on the overall schedule. Finally, it is shown how the robustness of a shutdown schedule is affected by introducing different amounts of slack.