The cleverer managers I've worked with typically include a factor of ~ 70-80% on worker office time. So in a typical 8 hour work day, 6 of those hours would be productively spent on a task at hand.
For an engineer who is sitting at his or her desk, focussed on a single task, I think this is reasonably accurate. Obviously there are a lot of things in an office environment which can further conspire to reduce the amount of productivity much, much lower.
For an engineer who is sitting at his or her desk, focussed on a single task, I think this is reasonably accurate. Obviously there are a lot of things in an office environment which can further conspire to reduce the amount of productivity much, much lower.