William Gibson's writing schedule isn't fixed. It changes shape as a book progresses, starting calm and ending demanding, and he's described both phases in detail in interviews.

The Direct Answer
Roughly ten a.m. to five p.m., five days a week, early in a book. Up to twelve hours a day, seven days a week, near the end.
Gibson described the shift in his 2011 Paris Review interview, along with the midday nap he treats as essential to the work.

The Calm Version

While actively writing a book, Gibson gets up around seven, checks email, has coffee, and does Pilates three mornings a week. He returns to the desk around ten or eleven and tries to write. If nothing is happening, he gives himself permission to go mow the lawn rather than force it. Most days, he's said, simply sitting down and trying is enough to get something started. The early stretch of a book runs roughly ten to five, five days a week, with a lunch break and a nap.

The nap isn't incidental. Gibson has said it's less about sleep than about the drowsy state right before sleep arrives, which is where he finds material shows up. It's an unusual thing for a novelist to name as essential infrastructure, but he's consistent about it across interviews spanning decades.

The Demanding Version

Near the end of a book, that calm schedule collapses. The workweek stretches to seven days, and sessions can run twelve hours. Gibson has described this closing phase as a kind of altered state that will dissolve if he doesn't keep feeding it, which means even downtime beyond sleep starts to feel risky. He's said the intensity isn't something he brings to every session by habit. It's a demand the book makes near the finish, and he lets the demand set the hours.

For the full picture of how his process works, from the typewriter he wrote Neuromancer on to his refusal to outline, see the complete William Gibson writing routine.

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