It would be nice to be able to use UDV as delay in Duration Assertion. Strange, that it is not possible while there is no problem with using UDV-s in Gaussian Random Timer or Reponse Assertion.
It's because the GUI validates the input field as a number, and ${VAR} is not a number ...
Changes have been committed to the 2.1 branch
This issue has been migrated to GitHub: https://github.com/apache/jmeter/issues/1636