We determine the necessary and sufficient conditions on the metric and the
four-form for the most general bosonic supersymmetric configurations of D=11
supergravity which admit a null Killing spinor i.e. a Killing spinor which can
be used to construct a null Killing vector. This class covers all
supersymmetric time-dependent configurations and completes the classification
of the most general supersymmetric configurations initiated in hep-th/0212008.Comment: 30 pages, typos corrected, reference added, new solution included in
section 5.1; uses JHEP3.cl