The day you take a shorter walk can still keep a welcome appointment with yourself.

Habits usually break at the point where the full version becomes impossible. The walk you cannot do properly turns into no walk, and one skipped day is much easier to repeat than a shortened one. What keeps a practice alive is not the length but the fact that you turned up. Ten minutes on a bad day protects the hour on a good one.

When today does not allow the whole thing, do the small version deliberately rather than treating it as a failure. Decide your reduced version in advance so you are not negotiating in the moment.