Increasing the runtime of methods in a particular class

In a certain class, you need to increase the execution time of the methods. Will it be correct to set the set_time_limit () function like this?

<?php set_time_limit(3600); class AjaxController extends controller { // ... } 

Will this work properly for class methods when I create a new object of the AjaxController class?

 $aj = new AjaxController();