I've not read all the books talked about (yet) but Brandon has said that Hoid is not just hanging around on these worlds during the events in the stories, he has his own motives and goals, and is actively pursuing them while the main characters are following their own paths.
I prefer to think that the whole night thing is merely hoid keeping up expectations. in the mistborn books, as an informant, it makes alot more sense for informants to meet under cover of night. simple as that, most shady events happen at night. it'd be out of place to meet an informant during the day...
and in Elantris, it's even said in the text that the group of people that he is acting with has been used to doing things under cover of night for a long time, sure they don't have to any more, but if they are still used to it then it makes sense that hoid wouldn't bother breaking tradition eh?
my personal thoughts on his seeming inability to act before being sought out is that Hoid isn't actually limited by any normal sense, but he's trying to keep his involvement hidden from someone/thing else that might if he were to act any more heavy handedly notice him. he's the only person(thing?) we've met(knowingly) that can jump from world to world... but that doesn't mean he's the only one that can do it..