Morning definitely seems to be the most productive for me.
I am able to review ton of flashcards and get a lot of studying done.
However, the important thing I need to remember is that the quality of my sleep the night before dictates the quality of my morning the next day.
So I should aim to sleep by 8:30-9:00pm and then wake up fresh and ready to keep that momentum going.
The slowest flashcards for me have been the English to Japanese flashcards since I’m basically learning new data, whereas the Kanji flashcards are pretty easy since I’ve studied them before, so it’s more a matter of re-learning or reviewing data, instead of starting from scratch.