It's a simple mistake to make. Most of the time when some compares the time on their watch to another clock they are interested in if their watch is fast or slow relative to the other clock. The officer looks at the CCTV time then at his watch which is 12 minutes fast and writes that in his report. Later when he reads the report, he doesn't have the information of which clock was fast and presumes if must be the CCTV clock because that is the important one.
Once they have accepted the report that the cctv clock is 12 minutes fast, the times on the tape are then treated as hard facts that trump everything else. The whole debacle about the postal police arriving before the 112 call may have been reconstructed from the incorrect CCTV time (unless you want to believe that officer looked at his watch and remembered the exact time in court two years later without writing it down). Dispatchers writing times in log books must have made a mistake because it doesn't jive with the "known" facts.
This is why going over old ground can be very useful! They probably
did know that CCTV time was off, and had already made that mistake, as they would get Raffaele to 'agree' that he called the
carabinieri after the Postal Police arrived during the November 5th interrogation! Being as that whole line of thought was damned silly, in context of all the other calls they were making before--and what would have had to have been after--they must have had at that point reason to believe it was possible that had occurred, and might explain why they called Raffaele in that night.
The fact the Postal Police never saw any of those calls being made, that it was the Postal Police who ended up giving directions to the
caribinieri, that it's pretty dubious that were Raffaele and Amanda guilty they'd have wanted to bring
more cops to the scene, and of course if they only wanted to deal with the
carabinieri all they had to do was take the phones from the Postal Police and then just say they got suspicious when they tried to return them to Meredith--all that suggests the idea that Raffaele called them after the Postal Police arrived is insipid. They had to have a reason to come to such a counterintuitive conclusion, and I bet that's because they
had already screwed up the direction of the timestamp error!
If that cop saw the timestamp of 8:53 and screwed up the polarity and thus they ended up assuming that video was at 8:41, then as Bolint would point out they'd
eventually eliminate Amanda as being the figure in the CCTV video, (perhaps not yet knowing about/thinking about Popovic's testimony) but on November 5th they might well think that Amanda went to the cottage
before Meredith did,
and that Raffaele had lied to them about calling the
caribinieri before the Postal Police arrived, thus 'Our Heroes' think they have
hard evidence Raffaele and Amanda are involved, which causes them to put the screws to both of them. The stoned Raffaele 'admits' he called the
carabinieri afterward,
and that Amanda left him ('whatever dude') which very well might cause the police to line up Raffaele's
tiny dancer in their sights!
Thus I agree with you and Bolint, that timestamp probably did read ~8:53, when the real time was actually 9:03-9:05!