Hello all,
Thanks for posting in regards to the data usage showing on your itemised bills for individual days/hours.
There are a few reasons this may be happening, most 'smart phones' will access the internet each hour (or as enlli has advised) or during the hour to check for updates for the apps and services you may have on the handset. These can be for emails etc
You can try turning it off in the settings or follow the advice of Drjazz that may help.
Rob