How could i add more start date intervals to the calls module?

I would like to know how could i add more intervals of minutes to the start date of the calls, i know how to add more duration intervals, but what i would like to do is to be able to register start dates for the call by minute or by 5 minutes.

At Calls.php file there’s a variable called minutes_value:

var $minutes_values = array('0'=>'00','15'=>'15','30'=>'30','45'=>'45');

I tried adding the intervals and repairing the app at the admin panel; the variable look like this:

var $minutes_values = array('0'=>'00','01'=>'01','02'=>'02','03'=>'03','04'=>'04','05'=>'05','10'=>'10','15'=>'15','20'=>'20','25'=>'25','30'=>'30','45'=>'45');

But still no success with it.
Here’s where i want the intervals at Call module