You know it early on

I love waking up early and starting the day.

It really makes the whole difference if I am able to get 2 - 3 things done before 6 AM, for the whole day to feel productive (I have not done a thorough study, so I cannot say if it really is more productive or just feels that way).

To me, by 8 AM I already know if a day will be a great working day, and by 10 AM I can surely tell if a day will be an unproductive day.

Today is already a great working day!