JavaScript: get average time spent

Question

I coded a script (working) to get the amount of days between two dates. [ServiceNow]

var chg = new GlideRecord("change_request");
chg.addEncodedQuery("assignment_group=1234^ORassignment_group=12345^sys_created_on>javascript:gs.dateGenerate('2017-06-30','23:59:59')^state=3");
chg.query();

var x = 0;

while(chg.next()) {

  x++;

  var start = new GlideDateTime(chg.sys_created_on.toString());
  var end = new GlideDateTime(chg.closed_at.toString());

  var dur = GlideDateTime.subtract(start, end);
  gs.addInfoMessage(x + " - " + chg.number + ": " + dur.getDisplayValue());

}

This gets me the following output:

1 - CHG0000001: 29 Days 12 Hours 43 Minutes 
2 - CHG0000002: 3 Hours 20 Minutes 
3 - CHG0000003: 41 Minutes 
4 - CHG0000004: 78 Days 3 Hours 41 Minutes 
5 - CHG0000005: 22 Days 2 Hours 7 Minutes 
... 
...

Variables:

x = 1
chg.number = CHG0000001
dur.getDisplayValue() = 29 Days 12 Hours 43 Minutes

How can I get the average time using all entries? I am lost.

Answer 1

Thanks to Isaac I could solve it this way:

var milisec = 0;
while(chg.next()) {

  x++;

  var start = new GlideDateTime(chg.sys_created_on.toString());
  var end = new GlideDateTime(chg.closed_at.toString());

  var dur = GlideDateTime.subtract(start, end);

  milisec = milisec + dur.getNumericValue(); //time spent in milliseconds

}

gs.addInfoMessage(((milisec/x)*1.1574074074067E-8)); //format milliseconds to days and get average