All devices in a security system should run NTP and be synchronised to a master NTP time source. This includes cameras, VMS servers, storage systems, access control servers, and of course front-end client PCs and operator workstations. Ideally the master NTP time source should be local, as internet time sources are weaker evidentially and obviously require an open internet connection, which may not always be available.
It is worth noting that Windows-based systems are very bad at keeping time. (Even Microsoft admit this on their knowledge base website, saying that Windows is not suitable for use with time-critical applications). We recommend installation of a special driver to sync the Windows PC/server's hardware clock to the right time, and far more frequently than Windows does as standard. There is little point in having all the security devices correctly synced if the viewing/control/playback system clock is wrong.
Note further that all recordings of data (video, audio, ACS events, alarm events, meta-data, other data logging etc.) should all be timestamped with UTC time (Universal Co-ordinated Time) and then the local time-zone offset added at the playback/review/live view point. If everything is recorded referenced to UTC then the data is rock-solid evidentially with regard to time, even if some servers or workstations have screwed up their daylight savings time adjustments or time zone settings.
As we move into a world where more and more is being done in the camera and the central servers become less important, then it is even more vital that cameras are all capable of running NTP and are properly synchronised to a reliable (and verifiable) reference time source.