It is crucial to have the time set correctly on your CCTV system otherwise searching through recordings for a particular incident becomes quite difficult.
You can connect your equipment to the most accurate clock in the world using an NTP server.
NTP stands for National Time Protocol, you can read all about it HERE if you like that kind of thing.
The following video shows how you can sync your CCTV recorder to this ultra-accurate clock to ensure your recording time is 100% accurate.
The video shows how to set this up using the XRN range of Network VIdeo Recorders, this includes the XRN0808E, XRN1609, XRN2016 and the XRN2536