For the thinking it will take forever...let him use a timer/stopwatch.
Maybe share with him this story...I dread unloading the dishwasher. One I don't like the reaching involved but mostly I feel like it will take forever. I finally timed myself and it takes between 6-9 minutes to unload. I break it into 3 jobs, silverware, top rack, bottom rack....and know each of those small tasks will take 2-3 minutes at the most depending on how focused I am or if I am interrupted.
He can do the same thing...collect data on how long certain tasks generally take (and break big tasks into smaller pieces) and then he knows basically this type of assignment takes around this amount of time.
