When Jesus entered Jerusalem, He got the attention of Jews and even Gentiles (people who are not Jews). Jesus impacted a lot of people. Some of the Greeks who came wanted to see Jesus, so they told Philip, who then told Andrew, who then told Jesus.
In response, Jesus told the two disciples that "the hour has come" (12:23). Previously, Jesus kept talking about the hour (AKA a specified time period), but at that time, the hour came. During that hour, the Son of Man should be glorified (12:23). A few verses ago, Jesus got glorified when he entered Jerusalem. But there is another sense that Jesus is referring to.
Jesus made another analogy about a grain of wheat. Jesus talked about how the wheat remains alone until it falls into the ground and that after it "dies" the wheat produces much grain (12:24). Note that the Greek word for "die" (Strong 599) has been used in Greek to refer to seeds planted before growing. The analogy references how Jesus would later die on the cross. Through the death on the cross (as well as the resurrection), Jesus takes on the penalty of humanity and rose from the dead to demonstrate the defeat of death. This in turn signals a confirmation of Jesus's sayings and his offer of everlasting life for anyone who believes in Jesus and what He did on the cross.