In learning theory and skill acquisition, research supports that several shorter sessions equate to better skill/content retention that one long block of time. So perhaps its not the amount of time, but how you divide that time.
Also, its about the quality of that time. Many people spend many hours at the dojo and on the mat, but not really training (more socializing). So you may also have to qualify the intent and intensity of the quantified clock time and number of days.
As in running, more is not necessarily better. Too much, too fast, too soon often leads to overload, lack of progress, and early burn-out.
Human engineering for skill acquisition is an interesting topic. Please keep us posted on your findings.
Adding to this, self-awareness is also important. You need to be fully aware of what you think you are doing right or doing wrong and reinforce the good and change the bad. Blind repetitive practice will do more harm than good. I've seen a lot of people just go through the motions for the sake of completing a technique. As Einstein describes; Insanity is doing the same thing over and over again and expecting different results.