There are many ways to do this. Here is one-
var StartTime = "11:10:25";
var EndTIme = "11:20:45";
var t1 = new Date();
var parts = StartTime.split(":");
t1.setHours(parts[0],parts[1],parts[2],0);
var t2 = new Date();
parts = EndTIme.split(":");
t2.setHours(parts[0],parts[1],parts[2],0);
var datediff = Math.abs(date1 - date2);
var timediff= datediff.toTimeString();
var result=timediff.split(' ')[0];
Haven't executed this but something like this should work.
Reference:
http://stackoverflow.com/a/6632849/1006297[
^]