This question is asking for an answer that is a quantity of time before an event. For example: "How much longer until the concert begins?" "How much longer until we arrive at the ocean?" "How much longer until dinner is ready?" I don't really think of it as an abbreviation, but I suppose you could think of it this way: "How much longer (do I have to wait) until the concert begins?" "How much longer (do I have to wait) until we arrive at the ocean?" "How much longer (do I have to wait) until dinner is ready?" Does that make sense?

“How much longer do I have to wait?” Is correct. “How much longer do until I have to wait?" - you cannot use “do” before “until” in this situation, and “until” in this sentence indicates that you are going to wait awhile and THEN start ‘waiting’ which is an unlikely situation I think. Your pattern above is correct of “how much longer until” + subject + verb. Here are some more examples: How much longer until I can eat? How much longer until we get there? How much longer until this is over? If you want to use the verb ‘do’ in the auxiliary sense of ‘must’ with this initial phrase you can’t use “until”. “Until” indicates something in this future and doesn’t work with this phrase. Some examples: How much longer do I have to sit here? How much longer do I need to wait? How much longer do you think you’ll be? (If you really want to work them both into a sentence you could potentially say something Nd like “How much longer do you think it’ll take until you’re done?” But you still need a subject+ verb following “do”)