Automatic Update of Filter with "Variable Input Field"

Hi, i am trying to build a Input Field where you are only allowed to start the Workflow with the execute button next to the Input field if you enter a valid date.
therefore i connected the Input Field to a hidden Filter which changes the CSS of the Execute Button. But the hidden filter is only updated when i am clicking on it and is not being updated after any change of the variable. Is there a way to force the update of the filter without clicking on it?