Clocks and watches appear so often in Murder Mysteries that they deserve a page all of their own.
Time as an Alibi
In the 1975 episode of Columbo called Identity Crisis time appears in the alibi of the villain in two ways. The villain claims that he could not have been present at the murder scene at the time in question because he was at his office recording a speech for a client into a dictaphone. He leaves this on the desk of his secretary, who will type it up for him the next morning. In the background Columbo hears a clock striking, which is supposed to put a time stamp on when the recording was made. However, the villain reset the clock in question and it is clearly not irrefutable evidence. Background noses in recordings are regular alibi and evidence features.
The real evidence is also a sound on the recording. Early on the murderer closes the blinds to stop the sun coming in. The window in question faces towards the sunrise, so Columbo knows that he was not there in the evening but early the next morning.
The Reset Watch
This idea often comes up in murder mysteries. During a violent death a watch might be smashed at a specific time to suggest when the murder took place. If a cunning murderer sets the time for half an hour earlier and then heads off to the location of his alibi and makes sure he is seen then he might be able to claim to have a solid alibi. However, if someone makes a big noise about being somewhere then the investigator should be suspicious.
Two interesting possibilities. 1. The victim if left handed and therefore wears his watch on his right wrist. 12% of people are left handed (interestingly this has not changed throughout evolution - source QI). The murderer removes the watch but without thinking puts it back on the more common left wrist.
The second possibility again comes from Columbo. This time it is in the classic Fade In To Murder starring William Shatner. The victim works in films and has the habit of running his watch five minutes fast. Of course, when the murderer resets it he does not take this into account. As always, the detective finds out.
The Train Ticket
Now this one is used in one of our own productions, but there are versions of this trick in various other murder mysteries. In ours the suspect leaves the crime scene and can prove it because he uses an Oyster Card. His journey would be registered on the automated system. However, he jumps of at the first stop and buys a ticket for cash to return to the crime scene. The suspect makes a big fuss about proving that he departed when he did, and many teams accept this at face value. However, some teams also want him to prove when and where his journey ended. Obviously this is much harder for him to do and his protestations about forgetting to touch his card only make him more suspicious.
A more clever murderer would not have used his Oyster but bought a return ticket using a credit card. Then the investigator would have to ask whether he had an Oyster Card and, if so, why he did not use it on this occasion.