Is possible to register click only in case user stays on page more than 30 seconds ?

Yes, It is possible to customize click tracking code so, that the click will be registered after 30 seconds of staying on destination page.
Example of such delayed click tracking code could be (with bold is marked change):
<script id="pap_x2s6df8d" src="https://localhost/PostAffiliatePro/trunk/server/scripts/clickjs.php" type="text/javascript">
<script type="text/javascript">
In this case we just added setTimeout javascript function, which delays execution of function papTrack for 30 seconds.
If user will leave page sooner, click will not be tracked !

In this way you can give commissions to your affiliate only if user, which clicked on your link will read the page at least 30 seconds.

I hope this easy trick will help you to filter some fraud clicks :-)