While I can't attest to this helping me focus, I can confirm that it does something.

I used to take it in the morning and evening. After stopping for a bit and restarting, I noticed I was waking up super tired and having intense dreams. I stopped taking it in the evening and confirmed that other people have had the same experience.

FYI I take it in a tincture, and I have not experimented with different brands or preparations.