That’s a good question, but it’s hard to answer because everyone has different views on this. I don’t see Facebook as a place where I keep up with my friends, I see it as a place where I keep up with everyone that I meet. I usually don’t go hunting for people, but I don’t see anything wrong with people adding me several hours after we met. Other people are much more protective. If you’re worried, give it a buffer of a day or two in any situation.