OmniFocus allows you to assign estimated durations to actions, action groups, and projects. Estimating how long something will take gives it more definition and helps ensure you don’t take on too much work all at once.
This plug-in calculates the total time of everything you select in the outline and informs you of any selected items that don’t have an estimated duration. For example, if you have a Today perspective that shows you all the actions you’d like to complete today, you could switch to this perspective, select everything in the outline, and use this plug-in to calculate the total time these actions will take and to identify actions that are missing a duration.