Honestly, whichever works better for you.
some research says morning is better, about 2 hours after you wake up as the nervous system is fully functional by then, and you'd had a chance to eat some protein and carbs for pre-workout nutrition.
other research says that 10 hours after waking you're at your peak, which for most is shortly after their 8-5pm job gets over.
so whenever you can get it in, while eating properly during the day, and post workout nutrition...will get you the best results.
