Adding additional values to duration fields

The following script adds the new option "42 Minutes" to the actualdurationminutes field in a task:

var duration = crmForm.all.actualdurationminutesSelect;

var tables = duration.getElementsByTagName("table");
var table = tables[1];

var row = table.insertRow();
var newOption = row.insertCell(-1);

var newValue = "42 Minutes";
newOption.setAttribute("val", newValue);
newOption.innerText = newValue;