When my cat unexpectedly got sick and needed care, for instance, I did not even schedule any writing sessions for a week.
Currently, if I have a particularly challenging week ahead such as a grading week or student-conferences week, I schedule my brief writing sessions (usually 15-20 minutes, at least 3 times a week) in the morning before work. When my cat unexpectedly got sick and needed care, for instance, I did not even schedule any writing sessions for a week. Long story short, recognizing my limits and day-to-day reality has played a crucial role in not only establishing a writing routine but also in maintaining it.