you during those hours. you can also note to others in your life that you are working during those hours, so you are not, in fact, available any time just because you work at home. not that they won't call you or drop by anyway, but at least you can refer to your office hours.
flexibility plays in when you have to run out to pick up your sick 7-year-old at school at 11 a.m., so you start back up at 1 instead of 2. or maybe there is a school play or field trip, so you work evening hours to make up for the time lost during the day.
when you 