A "good" manager can at least broadly know how long something will take, and not accept "40 hours" for a 1 hour project. A good manager may not be able to know that a 40 hour project will only take the employee 30 hours, but at that point, who cares? Is the employee sandbagging an extra 10 hours that problematic? Do we really need employees correctly estimating time to completion as perfectly as possible? Is an employee completing a task the company wants them too, ahead of time and on schedule, with a few extra hours to decompress or live their life really a disaster scenario?

What happens if the employee says "30 hours" and if it takes them 40. Do managers/organizations then move things back, or do they expect things done by the deadline given previously, even if it means putting in overtime to get it across the finish line?