Well, after one day a whole lot of nothing has happened. The mixture does smell strongly, but only of ammonia. To test if any sulfide had formed I withdrew a small volume from the reaction vessel and acidified it with hydrochloric acid. There was a hint of a foul smell, but I cannot say if it came from the experiment or my own fart. Bad timing.
Anyway, I would have expected the mixture to have taken on a orange-red tone by now if anything had happened, but it looks just as yellow as it did last night. Sorry to say, but so far it seems there's little truth to this, as I suspected. I will still leave it for a full week though.