Two. Sleep, and the shape of the day

Depression pulls sleep apart in both directions. Awake at four, or twelve hours and still exhausted.

What matters more than the total is the shape. A day with no fixed points, where getting up and eating and sleeping happen whenever, is a day with nothing to hold onto, and the hours spread out.

You do not need a strict routine. Two fixed points is enough to start. The time you get out of bed and one meal at roughly the same hour.