Delay asynchronous validators in angularjs

I have the following directive:

.directive('validateAsync',
  ['$http', 'API_LOCATION', function($http, API_LOCATION) {

  return {
    require : 'ngModel',
    link : function(scope, element, attrs, ngModel) {
      var apiUrl = attrs.validateAsync;

      function setAsLoading(bool) {
        ngModel.$setValidity('asyncLoading', !bool); 
      }

      function setAsAvailable(bool) {
        ngModel.$setValidity('asyncAvailable', bool); 
      }

      ngModel.$parsers.push(function(value) {
        if(!value || value.length == 0) return;

        setAsLoading(true);
        setAsAvailable(false);

        $http.get(API_LOCATION + apiUrl, { 
          params: {
            value : value 
          }
        })
        .success(function() {
          setAsLoading(false);
          setAsAvailable(true);
        })
        .error(function() {
          setAsLoading(false);
          setAsAvailable(false);
        });

        return value;
      })
    }
  }
}]);

Which is called like this:

<input ... validate-async="api/endpoint/to/check/validity">

It works great, actually too great. As it fires of a request on every keydown.

How could I make the directive wait like 300 ms before validating the input or make it fire the validation on input blur ?

Update

It was easier than I though: adding ng-model-options="{ debounce: 300 }" did the trick.

Thanks JB Nizet for leading me to the right answer