Sagan wrote for two-three hours each day. To come up with such a schedule it is perhaps necessary to try out different times of the day and then stick to the time that works best.
Sometimes we don't have that kind of freedom and need to accommodate our writing schedule to our life circumstances. This is one of the themes in the book Miss Iceland by Auður Ava Ólafsdóttir.
I love the back to school energy of September and to stack up on new school supplies such as notebooks, pens and class schedules. Instead of plotting in math lessons and homework I plan my writing time and choose the books I want to read.
When I make a plan for the year it is a lighthouse shining in the calender. When I plan for the month I make sure to make an appointment with myself that shines and flicker like a candlelight.