In this paper, we propose when and how to perform sustainability assessment during software product and service inception, development, and evolution.We explain the challenge of right timings for sustainability assessments, how they are often delayed due to missing focus on values during the early development phases. We refer to a current solution, called SusAF, and discuss some of its challenges. We wrap up by advocating for a legal regulation supporting the actual implementation of sustainability assessments alike with how they are required in civil engineering.