So given an event i of this type we may constrain another event j to stay between a time window with respect to i, so that finally we constrain the schedules t_j and t_i of the events j and i as in the picture with T the period and z_ij integer variables which take care of the modularity of the phenomenon. Then we have to find a feasible schedule with respect to these bounds. Unfortunately, this is an NP complete problem.