Rost
Legend
Platinum Level
For me, poker is a hobby, so I play when I have such a desire, when I have time for it and when I am in a suitable, good mood. Maybe it's better for my brain to play in the morning, but for me overall it's better to play in the evening.
userX
Visionary
Platinum Level
In my opinion, evening is a better time than morning. In the evening, when all the work is done, you can spend a few hours playing. In the morning, when you have a whole day of important things to do, playing poker is like not really understanding your priorities. Besides, in my case, the main most promising tournaments are held in the evenings.
john_entony
feed the Fox
Loyaler
My game is not dependent on my brain functioning, as I am motivated and play equally well at any time of the day. I only get worse when there is an air alert in my city and I hear explosions outside my window. 
dzsire
Legend
Platinum Level
It's definitely better for the brain than anything else, everyone is fitter after waking up (usually). However, poker tournaments tend to be held in the evening, so there's not much chance to play in the morning hours. (As an ordinary person, besides work, of course)