Back on topic.
This is O'Sensei's opinion for how long you should be training before Shodan(lowest grade, first grade):
"In your training do not be in a hurry, for it takes a minimum of ten years to master the basics and advance to the first rung. Never think of yourself as an all-knowing, perfected master; you must continue to train daily with your friends and students and progress together in Aikido"- O'Sensei
I don't get how that is Osensei's opinion on a grading system that was largely being built by his son at the time. He mentions mastering the basics
and taking at least ten years to reach the "first rung" - not first dan (I wouldn't mind seeing the original Japanese that John Stevens translated). In any case, the founder handed out plenty of third dans within ten-year periods and shodans
even sooner. Saito sensei also said that one doesn't master the basics until sandan
. It seems to me the founder's warning was to the student focusing merely on rank rather than attaining the basic skills of the art.