Javascript DateTime Set Ignores Time

Hi, this is a simplified version of my problem;

The code below carries across only the Date portion of the DateTime value (both controls are set to show both Date and Time) - I would like it to copy across the Time too (if it makes it any easier, I don't need the event to fire on time change).

 var sourceDateTime;
 var destinationDateTime;

 NWF$(document).ready(function() {

 sourceDateTime = NWF$("#" + sourceDateTimeVar);
 destinationDateTime = NWF$("#" + destinationDateTimeVar);
 sourceDateTime.change(function() {

     destinationDateTime.val(sourceDateTime.val());

 });

});

 I am using the 1.4.1. Any advice would be greatly appreciated.