As part of his bid, the builder prepared a preliminary schedule (sometimes already quite detailed). The main objective was to define how constraints, if any, were to be taken into account, so as to mark out all project deliverables in time, along with the means to achieve them.
When the contract is signed and the project enters the execution phase, the schedule must be fine-tuned and optimized, taking into account available resources, the final industrial layout and contracts with key equipment suppliers.
Contracts include penalties for delays, and may also include bonus provisions for adherence to schedule (although these provisions are generally rather difficult to apply, due to the shared responsibility between builder and customer, particularly in complex projects).