I have heard shakuhachi students discuss how long you should be able to hold a note, or how many pieces you should be able to play, or...
In approaching shakuhachi in an acheivement-oriented way, I think you can miss one of the great pleasures of the instrument: letting go of "result thinking." The goal is not to play ro for 45 seconds, but to practice the discipline of ro-buki (blowing ro) almost every day. The goal is not to master x number of pieces, but to dive as deeply as possible into the piece you're playing right now. The goal is not to get somewhere, but to find equanimity right here, through the music. That's what shakuhachi can teach.
I look forward to a day when playing shakuhachi is thought of more like yoga or tai chi. Unless you want to become some sort of TV personality, you don't go into yoga class saying to yourself "I really should be able to hold that hand stand for five minutes."