sort Cart by a Product Option DateTime Field

Hi

on my Productpage i have an Options Type Field (Date & Time).
If i add this product to the cart.tpl(basket) it will show me the DateTimeField (what i have entered) and any other option of the products.

Now i want to sort that cart basket List in desending order of the product options field date-time, so that the cart looks like this:

cart.tpl
Date | Time | Product | the other Product Options
-----------------------------------------------------------------------------------------
15-02-2012 11:23 | Product A | High Bass
11-02-2012 09:34 | Product A | Low Bass
08-02-2012 17:32 | Product B | Green-Red

The DateTime is set from the ProductOptionsField if i add this to the cart.

1.5.1.3 Version i use
Tried this for weeks from every angle, but any Idea how i can solve this? Any Help very appreciated.

best
Ralf