Sammy01 - I wrote an epic reply to answer further some of your post, but the 10minute edit limit kicked in and deleted the whole lot. I will retype this and post again shortly.
My view is that it's not worth pursuing. You could try writing to the judge's associate and asking if it can be changed under the slip rule, but if they refuse, then you are better off just taking it on the chin. By the time you go to mediation, file an application and get in front of the judge again, that six-month period will likely have passed anyway, and the Court won't be pleased about wasting very precious time and resources on a) something that is relatively minor and b) something that is temporary.
And are there any further provisions for more time? Is there an "or as agreed by the parents in writing" order? Are you at least on emailing terms with your ex?thatbloke - These were final orders brought about as result of a magistrates judgment after a full trial.