I just spent most of the last 20 hours sleeping. Sure it wasn't straight, I ate, used the bathroom, even browsed the forum on my phone briefly. But I would conservatively guess that at least 15 of those hours was actually sleeping. Also, what is the proper way to greet someone if you wake up at 9 PM? It may be your "morning" but it is physically well into the evening and many people are heading towards bed. I like the concept from xkcd of saying good morning from wherever on Earth is is actually morning, but that requires timezone math and geography quickly after waking up.
Well, since majestic lions sleep for that many hours in the day (albeit, disturbed by tourists and zoogoers), I'd say you're a lion. c:
Same here. No matter if I have a day shift or night shift, I always say morning to greet peeps. It just sounds nicer.