Given a project plan as directed graph $ G = (V,E) $ with activities $ V $, time lag relations $ E $, are weights $ \delta_{ij}, (i,j) \in E $ and starting times $ S_i, \forall i \in V$.
Formulate the optimization model of the Generic Time Scheduling Problem
with the objective function to minimize the sum of the (unweighted) starting time (WST objective function):