How to make a Count Down timer?

How can i start a count dow开发者_高级运维n timer on my application start and close application at certain time?

You should have a look at NSTimer. Read the documentation, it's not that hard to use.

When the timer fires you can exit the application. You find more information about that here:

Proper way to exit iPhone application?

As the most upvoted answer says, you shouldn't, but it certainly is possible.

If you need help with NSTimer let me know.