A job is called just-in-time if it is completed exactly on its due date. Under multi-slot conditions, each job has one due date per time slot and has to be completed just-in-time on one of its due dates. Moreover, each job has a certain weight per time slot. We would like to find a just-in-time schedule that maximizes the total weight under multi-slot conditions. In this paper, we prove that this problem is NP-hard.