Not unusual in my experience for CCTV systems time clock to be wrong, especially as regards DST and for no one to notice or bother (or know how) to fix it.
I have seen CCTV systems lose time during extended blackout periods when they are not backed up by a battery, and even if they are the battery run time is limited to maybe a few hours depending on the size of the system. (My 7 camera system can run for only about 3 hours on battery alone.)
In 2014 DST officially began on 5 October, which is some 3 weeks after William was reported missing, so I guess that rules out DST, but the system time could still have been wrong for various reasons.