I used to write for long stretches early in the morning when I had a regular schedule. Now that I'm in a new house with a new housemate and we're still settling, I write whenever it gets quiet and I manage to sit down. I need at least 20 minutes to settle in and get going but then I can usually focus if I don't get interrupted.
I like when I can set aside a regular timeslot. My brain gets very cooperative when that happens and it's easier to move through longer written pieces for me that way.