25: About a minute before 25, Holly becomes aware of a third man at the scene of the crime. Holly wants the porter to talk to the police, the porter's child plays with his ball. The porter will die later because the criminals don't want the police to know the truth. The birth of something new.
45: Porter agrees to meet with Holly and turns and looks frightened as he becomes aware someone is in his room offscreen. We suspect the porter hasn't long to live. In the next scene, Anna asks Holly about Harry Lime and we're more aware that Anna really loved Harry and that Holly hasn't much chance of establishing love with Anna. Now that I'm aware.
60 and -45: The police offer evidence to Holly, and Holly believes the police. He now understands that Harry, his good friend, has been involved in murder. From the start of the movie, Holly was trying to establish who killed Harry and believed that Harry was innocent, but the facts have completely changed his beliefs and he's ready to move in a new direction not for Harry but against him. There's no going back.
-25: The famous scene in the Ferris wheel where Orson Welles says people are happier dead and the line about the cuckoo clock. Holly understands that his life is in danger and a former friend could kill him. The final turning point.