Wise words from Douglas Wilson for writers who have a family to care for, taken from his new book Wordsmithy: Hot Tips for the Writing Life (Canon Press, 2011), page 40:
I have read enough books to know that the “Acknowledgements” section frequently includes a tribute to the wife and kids, who always let Dad go off to the study for the interminable time it took to produce the book. This is a reasonable thing to acknowledge, of course, but I would encourage writers not to overdo it — the disappearing that is, not the acknowledging. When an extra load develops, try to have it land on you and not on the family. If it has to get done now, then get up at five, and nobody else pays. So if you need to, get up at five, but always try to go home at five.
Think of it this way. A 60-hour work week is an honest job and a significant load, but a lot of the problems that come to people who work this much happen because of where those 60 hours are placed. Apportion 40 hours to your regular job, the calling which pays the bills, and then 20 hours for your half-time job of getting a writing career started. It is possible to work those 60 hours and still have lots of time left over for family. A week has a total of 168 hours in it. Sixty hours of work leaves 108, and 8 hours of sleep a night take away another 56 hours, leaving you with 52 hours a week to play tag in the backyard with the kids.