Yeah, does seem more likely it's my brain knowing the time fairly accurately from the early morning light levels, bird song, traffic noises, temperature, smells

Yeah, does seem more likely it's my brain knowing the time fairly accurately from the early morning light levels, bird song, traffic noises, temperature, smells in the air etc, and other cues I'm not consciously aware of, than that I have a timer, accurate to a few minutes over 9 or 10 hours, in my body.