Hmmm, well, we tend to look at skill, dedication and take into account time aswell, how ever time shouldnt b too important, if u have a skill of a 10th dan black belt doesnt mean u should b a 10th dan, how ever i mean that, if we can c progress in ur movemnts thought and strength then we will look into grading u, not b4, we have to look for these increases b4 we grade, we dont look at the time diffrence, how ever there usualy is a standard time diffrence, but never do i look at a student and say three months and so forth