I have suspected for maybe two decades and a half that our disturbed sleep might be associated with altered circadian patterns of many metabolites. This was my concern in the late 90s when early morning urinary metabolites were first being looked at. Change the time, or have patients with altered circadian patterns, and you might get different results. We cannot yet be sure that our results will be stable over the course of a sleep-wake cycle. This needs to be established, or an optimal time of day or sleep-wake cycle needs to be determined.
[Edited to correct how long its been.]
