Not two months
We watch as Hamlet grieves over the death of his father, the King inside of a tower. While on the outside, we see his mother the Queen go about her everyday life as though nothing has happened. The imagery juxtaposes Hamlet's depth of sorrow compared to his mother's joyous new relationship with Claudius. And thus reveals plainly the conflict between Hamlet, Claudius and his mother.
Yorick
We watch as Hamlet speaks to Yorick's skull. He was the former Jester to King Hamlet. The imagery reveals how all joy and jest have died in Hamlet as he lives in a time of murder and great consequence. We also see Hamlet's tenderness towards Ophelia as he asks the bones of the man whom he loved to go to Ophelia now and cause her to laugh. This shows us he still loves Ophelia.
The Ghost
Zeffirelli creates the famous ghost of King Hamlet speaking to his son in a realistic manner. We see a very real King recount his death before his son before disappearing into the night. This imagery creates for the audience the very real cause which Hamlet must unfold. Seeing his father in the flesh is far more compelling to the reality of what he must do, and it also plays into the potential for Hamlet being mad (did he see the ghost or not?).
Murder
We watch as Claudius witnesses the players perform before him. They perform something like the murder of King Hamlet, which the Ghost of the former King has recounted to Hamlet as having been done by poison in the ear. King Claudius reacts horrifically to seeing this, and the imagery shows us that Hamlet's instinct is correct about Claudius and shows us that he is hunting the right target who murdered his father.
