I would have to say it depends on who the unannounced drop-in is. I have friends who I adore and would welcome anytime, night or day, without hesitation. However, I had someone (two someones actually) ring my doorbell at 9p.m. on a Sunday to see me. I had neither seen nor heard from this person in over 8 years and the last time we had spoken, it was not great--I was annoyed and via the intercom in the building, I asked them to call me and I did not let them in. I never heard from them again. Oh well... it'd been years anyway and I really had not missed them in all those years...