time in ld???

I had a ld this morning, that was quite long. In the ld I thought how long it had alrady lasted, and calculated the time to be 15-20 min, then went off and did more stuff. When i woke up, I tried to wild back in, but just fell into a non lucid dream. Then when I woke up, wrote the dream down, but coyuld not remember much, and not too many details. And looking at it, it seems it only lasted 5-10 min, and I know i forgot stuff. I always write the length of lds in my DJ, so how long should I write that the dream lasted????