All Multi-photo Constraints are solved during the Global Optimization stage of Processing. These Constraints are not available if there is only a single photograph in the project.
Note: Constraints are not intended to correct gross errors in a project. For instance, if your model does not look very good because of misreferencing, incorrect camera parameters etc., then Constraints should not be used to correct for these deficiencies. First, ensure your model has basically the correct shape, then use Constraints if needed to refine the model.