There seems to be some confusion about the update time for the Playstation Store, partically with the case of the Modern Warfare 2 Stimulus Pack.
Ok, the store release dates have moved now, but the times haven't.
Store updates happen at 4pm to 5pm local time, thats your time.
Playstation UK Store Update: 4pm BST to 5pm BST
There has been occaisons when the store update times have been brought forward to 9am local time, but if the store does not update in the morning then it will at 4pm to 5pm, if there is a delay, Sony will annouce it on their blog, so please be patient
Hope this helps