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.
Inspiration to declutter paper piles, fall in love with a writing project and set up a writing date for Valentines.
If you want to try this writing practice out for yourself I made this free printable for you to download. It is a checklist on how to turn your own dream journal into a never-ending source for writing prompts and writing inspiration.