from http://stackoverflow.com/questions/20397253/implement-a-delay-on-scope-watch

timeout-watch-angular.js

    var timeoutPromise;
    var delayInMs = 2000;
    $scope.$watch("query", function () {
     $timeout.cancel(timeoutPromise);  //does nothing, if timeout alrdy done
     timeoutPromise = $timeout(function(){   //Set timeout
         $scope.loading = true;
         returnFactory.query($scope.query).then(function (returns) {
           $scope.returns = returns;
           $scope.loading = false;
         });
     },delayInMs);
    });