I think staying focused and being productive for 3-4 hours is very good. I think people without ADHD would be very happy maintaining concentration for that length of time.
However,it may be useful for you to take a break once it becomes no longer effective. Most people would disagree with me but I don’t have a daily routine. I know when it’s time, I just have to force myself to stop and do what I need to survive the day.
I hope this helps.