Philip (this time with one l)
some dojos: 1 lesson is 2 hours with no warmup
other dojos: 1 lesson is 1 hour including warmup.
There is no complete system - just a guideline, and most people tend to have far more hours of practice before a yudansha grading than the minimum requirement (guideline) of for example the hombu dojo.
If you have prior experience from other MA's (as you write) and this goes beyond the first couple of kyu grades, then you must have learned by now that it always vary. Each dojo has its own interpretation of the guidelines, and each sensei have their own reasons for pushing some student ahead and keeping other on a specific grade. Any MA is about personal and technical progression in a varying mix. It is impossible to say exactly how many hours/sessions/days/weeks/months YOU need to practice in order to grow enough in the right ways.
Like getting a drivers license. At least in our country there is a minimum of hours you need to have behind a wheel, but if you are still far away from being able to drive a car, then your driving instructor would surely suggest you postpone the test a while - or you are likely to fail.
I know people who had their body in the dojo for thousands of hours - never really progressing because their head was somewhere else - and i have seen people paying intense attention to every little detail and progressing really fast because they just loved every minute. Good and bad teachers is also a factor. so....
It dosen't really matter. Someone will let you know - or you will know yourself when the time is right. but waiting for having enough hours of training instead of just enjoying the ride would likely kill you enthusiasm.
Now go write you paper