Prison slang meaning you shouldn't need any explanation about the results of what you did. Whatever you did or do, it's going to get you beat the fuck up.
You stole from everyone, you snitch to the cops. Punk bitch, you know what time it is.
Basically a statement said to acknowledge how incredibly trashed someone is. You can say it to acknowledge someone else or you can say it to acknowledge how messed up you are.
If you are on another level of fucked up you can also respond that you are the clock. Who ever is the most fucked up is the clock.
A:"Duuuuuuuuuuuude!!!!"
B: "You know what time it is!"
A:"Do you know what time it is!?"
B:"Bitch, I'm the clock!"