I have also struggled with this issue. I wanted to restrict access based on time of day. In the end I decided the router was stable enough to depend upon. (It seemed to choose random times rather than work to a 24 hour clock).
I moved to DNS restictions using open DNS and used mac addresses to restrict times on the router. It is limping along but by no means seemless or user friendly.
I'm using plain GMT (Liberia - no BST) on the router Setup → Basic Setup → Time Setting and a valid local time zone on Voice → Regional → Miscellaneous. That may work for the original poster, but would reqire the time-of-day access restrictions all be specified in GMT/UTC instead of local time. See https://supportforums.cisco.com/thread/2217073
Any attempt to set both to local time gives badly wrong results, including incorrect time sent to the 'phone handsets.
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