I believe that you are talking about Act V, Scene 1, here. When you say that Hamlet and Laertes have been separated, you are talking about the part where they have been fighting in Ophelia's grave. They have been separated to keep them from fighting.
What the king says to Laertes is that Laertes should just be patient. They have their plan made for how they are going to kill Hamlet so Laertes should not get all upset right now. He will have his chance to kill Hamlet before too long.