My friend Dario has written one:

https://itunes.apple.com/gb/app/clock-check/id586663057

Clock Check — By Dario Persechino

Description

Clock Check is an application designed to aid CCTV engineers and Law Enforcement personnel when calculating the time discrepancies on CCTV systems.

The app calculates the difference between a ‘real time’ and a CCTV ‘system time’.

This difference can then be used within the app to calculate when on the CCTV system an incident should be searched for.

The app also provides a facility to save the details of checks for later statements or further calculations.