When we teach a new form or technique in martial art, we tell the student that they must execute the technique or movement at least 34 times before it becomes a part of the mental process to the point that it can be recalled with little effort.
This rule holds pretty much true for the average person. We also tell the student that the technique or movement must be exeucted with total focus for 300 times before the mental and the muscle execution becomes one. That is the point where the activity becomes nearly automatic, or instinctive. Additional practice is always desired as one progresses to an even higher degree of proficency.
I guess if the rule is in effect for martial training, I see no reason why it should not be just as effective for shooting a bow. If one was to practice 300 sessions, not arrows, with total focus to the execution of the activity for which the person is attempting to master, he or she should began to experience what you call muscle memory. One must remember that it is a gradual process, and like all things you get better with practice. It is not a mystical thing that says you put in 300 and now you are the second coming of Howard Hill! Progess will be gradual, most often with peaks and valleys. You will have times of great increase in skill, while the further you go up the skill ladder, you will not see those great jumps, but will continue to move higher, in smaller increments. Don't get in a hurry, it is not the destination that we should always desire as the goal. Sometimes the lessons are learn in the journey.
One word of caution, as stated above, it is much like a computer, junk in junk out. Put in the best you can muster, and you will receive the fruit of your labors.
I would suggest a regular session, such as 40 well shot arrows. Of course it could be broken down to practice on what you need to work on, such as working on your release by shooting at the target with your eyes closed at two or three steps. This will allow for the feel of the shot, the back tension, the pull through.