I'm at the same stage, and I reached out to the Warsaw embassy recently via email to see if they would give any updates, since I've been READY for a while now. Got back a form letter saying it can take a several weeks to receive instructions from them, and to please not schedule the appointment until we have been contacted with instructions to do so.
From old posts here and other forums, believe it'll be coming via email from Warsaw. I'll update with a more confident answer if I ever actually get something from them personally though.