A commonly accepted time frame for mastery is 10,000 hours
What context do you refer to as "commonly"?
As far as I know the amount of 10,000 hours in old Japanese and Chinese texts means: The whole life - plus one hour more. Wich noone can accomplish ...
In aikido, shodan gets people to the basic level of understanding of techniques. Nidan focuses more on pulling all that together in application. Sandan marks what is really the end of learning the "craft" aspect of aikido. Yondan is the beginning of the expression of the artform - and entering the ha stage.
Thank you very much: This simply is what I was asking for.
I don't really want to start this debate anew. Just let me say that this "requirements" or "standards" are clearly different in some points from what we have in our aikikai federation in Germany and also different from the criteria, Endo sensei sets.