I tend to start at 9 o'clock in the morning and write until 3. Those are my best hours. They fit the other rhythms of the world. So I write for six hours pretty much without any breaks.
You never know if you're a writer. You can't trust it. If you woke up and said 'I'm a writer ' it would be gone. You wouldn't see anything for miles - even the dust would be running away.