According to the PMBOK Guide, the project manager is responsible for developing the project schedule and estimating the activity durations. One of the tools and techniques for estimating activity durations is decomposition, which involves subdividing the project work packages into smaller, more manageable components called activities. By breaking down the project into smaller tasks, the project manager can better understand the scope, complexity, and dependencies of the work, and apply more accurate and reliable estimation methods. This will also help the project manager to identify and manage the risks and uncertainties associated with the project schedule. Therefore, the project manager should break down the project into smaller tasks and estimate the durations of the activities as the next step. References: PMBOK Guide, 6th edition, pages 191-192, 201-202.