The Chinese always pay a visit to their friends、relatives and colleagues . They will pay the visit to the one they want to without asking them beforehand. And they always have some crashers too. Well,if it is different in the USA. The American won’t pay the visit without preengaging. The friends and the relations will get together when the festival is coming. But in the other days, they should make sure the time before paying the visiting if they have something important to deal with. It is misbehavior if you go to somebody’s house without the permission. 
So if you go to the American’s , you should make sure the time at first and arrive on time.And if you want to invite the Americans to your home, you should give the formal invation instead of telling them “You are welcome to come my home anytime!”.