If you need to account for project manager's time spent, well, managing the project -- as opposed to performing project tasks -- you can use the Forecast Project Leadership feature. Same thing if a project will require X% of a senior manager's time.
From the Project 360 page, go to Project Settings then Resources. Then select the resource , the primary project role will pre-populate if available, and then enter the estimated percentage of their overall time will be allocated in this role. Two key points:
- Project leadership is forecasted in terms of percentage only for convenience and practicality purposes. It is applied for the duration of the project.
- You can override the project role for instances where, for example, a senior developer is assigned tasks for writing code, but they also happen to be wearing a project manager's hat. The estimated effort for both roles are included in the senior developer's overall forecasted workload.