I'm thinking about billing for office hours

I gather I'm not the only person who, because I work from a computer at home (technically, at my parents' home, but nonetheless not a clearly marked office), have friends come calling on me when I'm under deadline.

I love my friends, but I don't really earn enough money to drop what little I'm doing which does pay, just to sit and shoot the breeze with them.

I keep fairly regular hours on the computer -- out of deference to my parents, who do occasionally like to use the equipment they bought for themselves. I arrive at mid-morning (when I'm not already here, house-sitting), and, these days, I leave by 7 p.m. unless there's a problem which can't wait until morning. Those sorts of problems are rare.

Plus, two of my jobs have mid-week deadlines. I go nowhere on Tuesdays, or most Wednesdays before sunset (hissssssss! hide me from the crossssssss).

So, if I get a half-dozen calls or visits from friends, even though I've told them repeatedly that I'm not available for fun stuff during those set hours, should I send them a bill for the office visit? Would they get the message? Or, would they simply stop calling me and visiting me altogether? I really do enjoy their company, when I can play, so I'd be very unhappy if I drove them away because we couldn't agree on my schedule.