is it usual for bitches to go further than their 63 day pregnancy, my bitch mated late in her season(first litter) and due now but isnt showing signs,  will her eggs have been fertilised later and she is possibly now running one week later than i suspected? will i leave her another week or so and see if anything will happen, saying that shes a lot more mellow this week, eating fine and generally just a bit more dreamy.
any advice?

It varies from breed to breed and boitch to bitch.  I certainly would be panicking if one of my bitches went more than five days over, and sooner if I knew they were mated at the right time (only had one bitch go late when she was mated early).

Could it be that she is empty.  I would want her scanned to check that there are live puppies there.

My old Jack Russell was confirmed as pregnant then re absorbed the lot.  As Archer has said I would go to the vets and have her scanned.  I would be deeply concerned if mine was that late.