“How about your D?”
This is her last quarter with a lab, and so I think that’s 14 hours a week of classes.
When I ask her, she guesses less than for your D. Like maybe even as low as 15 hours a week for outside work, most of the quarter. And this hasn’t varied throughout her 5 1/2 quarters (except first quarter first year, when she took 3 courses, and wasn’t bored, but felt weird about how much less she was working than everyone else). But she may not be a good judge of how long she spends. She’s not very good with time. 
She does all of her reading by the discussion date, so that doesn’t build up, but she generally procrastinates papers and writes them very fast. There is some correlation between how long she spends on papers and her grade, but not a tight correlation.
When all of the papers fall at the same time (last quarter, 2 short papers, 4 long papers, and a big project, all due within 10 days, and this was before reading period), she is surely working a lot more during that period. But that’s usually just once a quarter.