Multiprocessor scheduling is a well studied NP-hard optimisation problem that occurs in variety of forms. The focus of this paper is explicit modelling of multiple task intervals. This work extends a constraint generation procedure previously developed for an avionics scheduling context. We here address a relaxation of the original problem and this relaxation can be considered as multiprocessor scheduling with precedence relations and multiple intervals. The explicit modelling of multiple intervals strengthens the formulation used in the constraint generation procedure and we illustrate the computational effects on an industrial relevant avionics scheduling problem.