Hidden Sidequests

[Crystalmaster Mike]

Well, DP hasn't so many places you can explore, finding rare items along the way. In fact, most of the time, you'll end up finding a mere Ultra Ball. But I did find something:

You know those empty houses you sometimes come across? I remembered stepping into one before and getting some item from a lady that was in, who was gone the next time I entered that house another day. Well, today (Friday, at ca. 10:20 AM), I stepped into the house on Iron Island, and Byron was there and after a little rant about his tough relationship with his son, gave me a Metal Coat before leaving!
So, if anyone knows the hour/day that someone appears in the other houses, could he fill me in?
The empty houses I know of are:

the one on Iron Island
the one in Canalave City, above the Sailor's house
the one on route 217, the other one being where you get some HM or PlateApart from those, I've found two things bugging me, and I'd like to know if they do something special:

The thirsty officer in the road house of Canalave City. Could just be a nostalgic flashback to RBY / FRLG, but has anyone succesfully offered him anything to drink? I always have Lemonade on me, but maybe this guy's more of a Moomoo Milk-type person...
The Psyduck in Snowpoint City's Pokémon Center: what's up with him? I tried the Secretpotion, but to no avail. Maybe it's just there to give me a migraine...
The cave in Celestic Town: any chance of anything appearing there when you come to it with the 3 Psychics in any order, or your coverbox Legendary, or Giratina for that matter?

[AdventureSerum]

Well, I do know that Giratina's in that horribly annoying haunted ruins-type place. I suspect it's just for decoration, but yeah, I really want that cave to do something cool too.

[Phoenixsong]

Hm. Well, the officer is just a nod to RBY the way a few other things in DP are, and I'd assume the Psyduck is just kind of there anyway. I doubt the cave in Celestic does anything... I mean, I've been sitting back here and waiting for Poké-Jesus to appear in the Hearthome church/temple/whatever and have so far been disappointed, so... I suppose you can try, but I don't think it serves a purpose.

The houses and stuff I didn't know about, though. I should look into those. (Dunno what I need a Metal Coat for... you can catch Steelix, and I already have a perfectly good Scizor... ah, well. Free is free.)

[AdventureSerum]

It really seems like they put that cathedral thingy there as if to say, "Ha! And to think that all this time you thought that the Pokemon world has no religion!"

You know what else drives me nuts? The little green area in the Pokemon daycare. WHAT IS THAT FOR?!

[RattataGuy]

It's technically not a church, but a place that celebrates pokemon the world over, or something like that. If you get a pokemon to hatch in there, it'll state that the location is "a foreign building."

[Crystalmaster Mike]

Well, I do know that Giratina's in that horribly annoying haunted ruins-type place. I suspect it's just for decoration, but yeah, I really want that cave to do something cool too.

Well, don't know if you know, but there are 3 items in there, too.

I went straight forward through every following room and ended up at Giratina.
Then I went through the left exit of every room and ended up in a room similar to Giratina's, but with a Rare Bone on the place where Giratina stood, IIRC. Same thing with going through each right exit.
Going down in each room, I found a different item.
Don't know though if when you go diagonal (left-up-left-up or something), you could end up somewhere else.

[AdventureSerum]

Maybe that green room was going to do something cool originally, but they took it out before they released the game. Hmmm.

[Blademaster]

That green room in the D/P Daycare is where the father Pokemon paces back and forth and smokes cigarettes while he's waiting for the female to lay an Egg.

[Crystalmaster Mike]

Maybe nothing special, but by saving outdoors in the Fight Area on a Sunday, you can fight your Rival on a Monday, since he won't have disappeared. This will only happen if you go inside or go to another town.