The TSV values are not available on object based portlets build on sub-objects like Assignment.
Steps to reproduce:
Release : 16.1.0
The time-scaled values (TSV) on the object based portlet work only with the first level master objects (eg. project). Assignment object being sub-object of project object the TSV for ETC field is not supported on the portlet build with assignment object. This is how the classic UI has been build to work.