It is unlikely that an organization will have all the resources required to complete a project in-house. Procurement provides an important function in project delivery even though it often has a reputation for holding things up and making things difficult. Internal stakeholder perceptions aside, an important aspect of project procurement is indeed timing. There are two project management concepts that contribute to this importance: Critical Path and Project Management Triangle (model of constraints).
Critical Path Method
A project consists of many tasks, some of which are independent (can be done simultaneously) and some of which are dependent (must be done sequentially). The critical path of a project is the shortest time a project can be completed and is created by the longest series of dependent tasks. When a task that is on the critical path of a project is delayed and/or extended, the whole project will have a longer completion time. In complex projects, shortening a task on the critical path may create a new project critical path.
Project Management Triangle
The project management triangle is a model of constraints that shows the tradeoff between three project elements: Scope, Time, and Costs. In order to make gains in one of the three elements, at least one of the two remaining elements must be sacrificed or else project quality will be affected. For example, if a delay in procurement occurs, either scope will have to be reduced or costs will have to be incurred to make up for the lost time.
Alignment between the procurement schedule and the overall project schedule will ensure that scope, time, and costs are optimized. Early involvement with project management will prevent timeline stress down the road. Here are some considerations with regard to timing for procurement:
The number of RFx packages or sourcing events – the larger the number of sourcing events the more coordination will be required. Understanding the supply market can also help because the number of sourcing events can be adjusted according to the market by combining or separating the scope of the packages.
Time required to complete RFx document – this is dependent on specifications, complexity, degree of customization, and size (larger contracts tend to require more time to put together)
Duration of sourcing event out on market – this has similar characteristics as the previous step only that it affects external rather than internal parties. Again, consider the quality and granularity of information required. Additional factors for bid duration are the competitiveness of the market, market convention (estimating departments might be used to a certain duration), and vendor availability as it affects how many and the quality of the bids that will be received.
The lead time of supply or the completion time of service/work - engineered and customized service/materials will take longer than standardized services and/or mass produce materials. Doing some research whether it is from historical data from your own organization or reference from other businesses will help you gauge a reasonable time required for delivery of the material/service.
Time required to evaluate and award – you might consider the personalities, experience, and workload of the team evaluating and awarding the contract. Having well-defined and agreed-upon evaluation criteria will reduce unnecessary effort or conflicts involved in evaluating bids. You should also include schedule/lead time as part of the evaluation criteria.
Onboarding time required - new vs old vendors will vary in the time it takes to execute the contract. If they are experienced in doing the work or even experienced working with you specifically, then it would obviously require less time than a new vendor.
You may also embed schedule controls directly into the contract by including contract schedule requirements (construction/services can be shortened with more resources) or required delivery dates (supply delivery may be shortened if materials are sourced from multiple/alternate locations or by using a faster mode of transportation). Alternatively, you may directly exchange money for time through liquidated damages and early completion/delivery bonuses. Keep in mind that the more demanding the RFx, the higher the risk that potential vendors will opt out of bidding. Be sure to have familiarity with the market when utilizing these methods.