Thank you very much :-)
I'm at day 5, daytime. And no, if I go in front of the house nothing happens.
I solved the riddle, the little cutscene plays (Adriana plays the guitar, talks to her brother about the papers etc.) and then I am back in the dining room. And after that I'm kinda stuck, because I haven't found a way to progress any further.
I opened the strange cabinet and now I can't progress further. Visited all locations, spoke to everyone - but I can't proceed. What did I miss?