The first one is pretty much WRONG. We very rarely (if ever) say it. The second one is correct, they are asking when you got here and started waiting. I disagree with two of the other posters, we do not use it so much for future plans. We are much more likely to say "how long are you going to wait" (That is the function of going to). In this regard I agree with Ana.

"How long are you waiting for?~" is asking how long they are supposed to be there waiting. "How long have you been waiting for~?" is asking how long they have been there.

How long are you waiting for?~ To express future plan, in this case the person is asking how many hours or minutes is the person planning on waiting. How long have you been waiting for~ expresses an action that starter in the past and is still happening now. In this case the person is asking how many hours, minutes days etc, the person has been waiting until now. I hope it helps :)

There aren't many situations for the question "how long are you waiting for?". There are many situations for the question "how long have you been waiting for?" Most commonly, this question will be used. Examples: "How long have you been waiting for a table at the restaurant?" "How long have you been waiting to get your dream job?" "How long have you been waiting for her to call back?" "How long have you been waiting for your car to be repaired?" Another question that is commonly asked is "how long are you going to wait?" Examples: "How long are you going to wait before you message him back?" "How long are you going to wait before you start your homework?" "How long are you going to wait before you finally speak up?" "How long are you going to wait before you get your driver's license?" I hope this helped!

is it correct to say "how long are you waiting for"? I'm not sure .