I could imagine someone stomping in the door, throwing a can of tomatoes at the refrigerator, and having his wife ask: "Where have you been all this time?" He would then answer: "I've been standing in line three hours for these tomatoes you wanted!" However, if the question is, "What took you so long?", the answer has to be: "I stood in line for three hours." Also, you can only use the former if purchasing tomatoes is the primary action of the last three hours; if you've been out for five hours and two were at a movie, you can't use it unless the movie is already known information to both parties.