For every activity vi of a job-shop scheduling problem an interval [fi,si] is given, meaning that vi cannot start earlier than fi and must be completed not later than si in any optimal schedule. The use of such intervals often accelerates existing algorithms. The paper demonstrates how such dates can be improved by an iteration procedure. Here, the values for vi result from the optimal solution of a one machine problem where operations may be interrupted. The influence of these [fj,sj] intervals on some fi is discussed even for the case where there is no order relation between vi and vj.
