Angular.js directive does not work for uib-tooltip

Question

I am struggeling with uib-tooltip. I would like to add there 'tooltip-popup-delav' using a directive.

export function UibTooltipDelay(): ng.IDirective {
 'ngInject';
 return {
  restrict: 'A',
  link: (scope: ng.IScope, element: JQuery) => {
     element.attr('tooltip-popup-delay', 500);
  }
 }
}

Attribute is added but it does not work... why?