How does Osric know this? Was this a scheduled visit? A previously arranged meet up? Was there a messenger that warned someone that these people were coming? Did that message get to Claudius? Was his plan to get Hamlet killed at 1pm and greet the visitors from Norway and England at 1:30? Would there be an advantage to getting Hamlet killed before their arrival?
Or did the message come to Osric in the midst of all the drama? Did he get it on the way between telling Hamlet about the fight and turning up to judge it? Did he have time to tell Claudius about it? I don’t think it’s a surprise visit. Obviously, Osric knows who it is before they arrive and why they’re making war sounds at each other. He didn’t get a text.
Would it be apparent from looking out a window? Where or how does Osric get his information?
The Hamlet Project 