I don't know. I am not smart enough to figure out how I can learn without training. So for me the answer is never. Even when teaching I try to emulate some examples set by other more senior teachers who work their own training in class (be it getting some ukemi practice with beginners or pulling aside a senior student and showing them some more advanced stuff and giving them the greenlight to go at me full bore, etc.)
I know my own teacher who is 8th dan has his own personal training time. It's either solo practice or practice with a few senior students when he is not traveling.
You need to train no matter who you are IMNHO.
There may be a time when I can't train. That would truly suck.
ow man that SUCKS
you really bummed me out!
oh yeah, I get to train tonight
peace