Meaning: to wait for a short time Examples: She told me to hang on, she would arrive in 10 minutes. I am in the middle of an important task, you need to hang on for a few minutes, and then we can talk.
Meaning: to stay at one place for a short time on the way to another place Examples: They stopped over in Singapore on their way to Australia. We stopped over at the grocery store on our way to my parents’ house.
Meaning: to stop working for the rest of the day Examples: It’s nice and sunny today, we should knock off early and go get some ice cream. What time do you knock off today? I want to take you to a movie this evening.