5.1 Time is one of the fundamental variables in every construction project, and perhaps the one that the parties have the least control over. This chapter concerns the Contractor’s time obligations under the FIDIC forms. It is specifically related to the construction period, that is the period from the date after which the Contractor is required to commence the design (if appropriate) and execution of the Works to the completion of the Works. In all the Books, the first is marked by the Commencement Date, which is notified to the Contractor under Sub-Clause 8.1 [Commencement of Works],1 and the second by the issue of the Taking-Over Certificate for the Works or, in the Gold Book, the Commissioning Certificate for the Design-Build.