Dopamine is one of those hormones that varies pretty strictly with one's circadian rhythms. Again, anything that modifies dopamine homeostasis (and that includes "indirect compounds" like the cannabinoids and nicotine), should respect this circadian pattern.
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I think it's great to pay attention to this when supplementing in general. However in this case, I can think of counter-examples where a supplement is said to help induce sleep by relaxation despite (or possibly as a result of) increased dopamine activity.