Morrison didn't write in long protected stretches with nothing else going on. She wrote a Nobel-winning body of work in the gaps of a demanding life, as a single mother of two and a full-time book editor. The how is mostly about where she found the time.

The Direct Answer
In pre-dawn hours and stolen pockets of time, around a day job and two children.
She was a divorced single mother and a Random House editor when she wrote her first novels, fitting her own work in before and around everything else, per her Paris Review interview.

The Day Job Came First, Literally

By day, Morrison edited other people's books. She was the first Black woman senior editor in the fiction department at Random House, and she championed writers like Toni Cade Bambara, Gayl Jones, and Angela Davis, plus Muhammad Ali's autobiography. That was a real job with real hours. Her own novels had to fit around it.

I had to write either in between those hours, hurriedly, or spend a lot of weekend and predawn time.

Toni Morrison, Paris Review, 1993

She was honest that she'd never been able to write on a clean daily schedule. The work happened in the margins of the calendar, in weekends and early mornings, in whatever was left.

Writing as a Single Mother

Morrison divorced in 1964 and raised her two sons largely on her own. She wrote her debut, The Bluest Eye, in fragments while doing exactly that. The pre-dawn habit came straight out of this reality. The hours before her kids woke up, around five in the morning, were the only ones nobody else had a claim on. So those became hers. She made coffee in the dark and worked until the household started to stir.

From Stolen Time to Deliberate Ritual

What's striking is that she didn't drop the squeeze-it-in approach once life got easier. She substituted compulsion for discipline, as she put it, which meant when a book got urgent she'd push everything aside and write in sustained bursts. The early start, born from a packed life, became a chosen ritual she protected for decades. For the wider picture, see the full Toni Morrison writing routine.

What You Can Steal