Work or Duration?
As a reminder, work is the length of time a task will take (e.g., 8 hrs), while duration is the actual time that passes before the task is complete (e.g., 2d).
I prefer to receive work estimates rather than duration estimates from my teams, so I understand the cost of the project. If the teams provide duration, they are already considering factors outside the actual task at hand, most of which is not billable, and leaving me with no idea what the real work effort will be.
Instead, I'd rather have the teams provide me only with the work hours required to complete each task, then I as the PM can factor in overhead, productivity factors, holiday plans, etc., to arrive at a final delivery date. This simplifies the estimation process, keeps the team focused on the task at hand, lets me know the real work effort, and helps ensure that estimations are determined consistently across tasks and teams.
I usually ask for estimations in hours (the default unit of measure for work in MS Project). Then, when I enter the work effort into Project, it automatically calculates the task duration in days (the default unit). Then I can see from the plan's critical path when the project is likely to end and make any necessary adjustments.