Dolphin style mon
...you'd have 8 hours out of 24 with your brain fully awake, 8 hours with only the right hemisphere awake, and 8 hours with only the left hemisphere awake. Not only will this let you spend 12 waking (ish) hours with each partner, you can also tailor the shifts perfectly so as to get the most apposite brain half to hang out with each partner. If you're a chap, then your -- let's be technical and call it your hippy hemisphere -- your yoghurt-weaving, basket-dying, tie-smoking brain meats half can spend its waking hours jus' chillin' with your manic pixie dream girl, and your, I suppose, scientist math-hemisphere can spend its waking hours with your xkcd-reading implausibly bespectacled nerdy hipster geekette, playing D&D and alphabetising your SF collection. It will be perfect...