Many serious authors establish and maintain a set schedule for writing. The timing is generally a product of their family/work schedule. Working folks may be obliged to write on weekends, or early in the morning or late at night, before and after work, respectively. Retired individuals have more flexibility—perhaps too much—because those with extra time on their hands tend to have trouble integrating writing with other tasks. Chores and vacation travel, among other distractions, may intrude on writing time.
It may help to carve out a consistent time and set a writing goal (producing a minimum number of pages per day, for example.) However, if writing becomes a job or a chore, creativity may be compromised.
The short answer to this dilemma is every writer needs to seek and find their own level when it comes to designing a writing schedule. Best to experiment and adopt the time and location which leads to the most prodigious and creative output.
So true!