BleepingComputer.com: When does a "click" register when clicking on ads.

Quick simple question really.
Let me explain.... i love free sites... mainly cause I got no money(plus a free ones provide much more help then the paid ones... i've tried once)..., but I do try to support them. And from my understanding their revenue comes from advertising.
Sooo... whenever I go to a site that is free I always click on the ads, and I wait,wait and wait till they load in....
... so the question is... how soon can I just close the window for my "Click" to register IT as a referral?