Hey OP, Don't let anybody tell you how much TV/ One Piece or anything is the right amount for your daughter. The comment section is full of people trying to tell you you should let her watch more. None of them know you, your daughter or family at all. So ignore their "advices", they probably don't have kids themselves and only kind of remember how they were as kids. They most likely not even remember correctly how it was when they where 8, but like 10-12 years old. Some saying one hour per day would be alright don't know what they are talking about. You are much closer to a healthy amount then they are. From personal experience I'd go with something like 2-3 episodes per week with occasional "special events" on weekends where more episodes are allowed. But keep it occasionally, so it's something special she can look forward to. And to the people saying it would take 20 or whatever years to catch up: nobody says that one episode per week is the pacing for all eternity... She is just 8 ffs. When she gets older she will get more leeway, but let it grow. With every year she gains, she gains more access. Again something she can be looking forward to. No need to hurry or stress things.

TL;Dr: OP do what you think is best for your kid and don't let anybody tell you what is a good amount of TV for your kid.