I had another this morning that was 5 or 6 seconds, but that's pretty long for me. Might have been the longest for me. It doesn't really matter the length or content, more the frequency in which you get lucid. Aim to get lucid often, and then work on quality. It's easier to work on something that you have a lot of time with, rather then working on something that you can only get to every now and then.