How to change value after delay by using angularjs?

Answer 1

You are making changes to scope outside of what angular knows about (inside a timeout).
So you should use $timeout.. otherwise you have to use $scope.$apply()

$timeout(function() {
    $scope.val = true;
}, 3000); 

http://jsfiddle.net/6uKAT/21/

For timeout use $timeout and it will call $scope.$apply() for you.
Likewise, for ajax use $http.

if you can't use these, then you must call $scope.$apply() yourself:

 window.setTimeout(function() {
     $scope.$apply(function() {
        $scope.val = true;
     });
 }, 3000);

Answer 2

Try using: $timeout

Angular's wrapper for window.setTimeout. The fn function is wrapped into a try/catch block and delegates any exceptions to $exceptionHandler service.

$timeout(fn[, delay][, invokeApply]);

Updated Fiddle

JavaScript

var app = angular.module('miniapp', []);

function Ctrl($scope, $timeout) {  
     $scope.val = false;
     $timeout(function(){$scope.val = true}, 3000);       
}