This is an interesting topic, but somehow it got reduced to quantity over quality, evading the real question: how many hours of training? And how are they distributed?
First of all I would like to explain properly and over simplified, the mechanism of motor learning which is the scientific term for what we are facing when we thing of getting good at shooting bows and arrows.
There are 3 important stages in this learning process.
The initial execution, and in this process the Cerebral Cortex is involved. This advanced part of our brain (evolutionary speaking) is able to quickly learn and repeat movement. So this is the stage, when based on observation, you see how someone raises the bow and releases the string. The Cerebral Cortex is the one that allows you to act the part. This element, applies in archery to learning form, draw cycle, conclusion (depending on coaching technique).
So now you act the part. This comes quickly, it is n necessary a minimum of 15 repetitions. With a minimum of a 3 to 5 minutes of break interval between each action. The break is not for you muscles to recoup, but for your synapses to consolidate. Because in this stage, you are literally building new neurological pathways in your brain. You get wired to shoot so to speak.
During this process the brain is highly susceptible, and anything that interferes with this process, can modify the memory consolidation. So introduction of new stimuli, auditive, cognitive, can alter or modify the learning process.
Afterwards, a period of 24 hours is needed in which that motion is not performed anymore. Sleep can be a factors, although most studies contradict each other at this chapter. My opinion is, if sleep is not needed for the Cerebral Cortex, than it is surely needed for the muscles to shape up. In this time period, the neuronal pathway is consolidated. So after 24 hours, in the next practice session, you are not susceptible to changes in your repetition.
Dangers: it takes twice the amount of repetitions to unlearn these actions if they are not performed correctly, if it is done right away, so in the same training session, at an interval no longer than 15 minutes. Hence the importance of coaching and observation of a new shooter to learn proper stance, form, grip, etc.
After the next set of repetitions. After 48 hours, entire sequences of the motor learning sequence, are distributed to different areas of the cortex. Meaning the whole shooting process is internalized. Now, this element is important as well, because now various subsequences of the execution are susceptible for training, on their own. So at this stage, the archer is working on one element at the time: foot position, bow arm, grip, draw, release. Also VERY important. The initial learning that occurs in Cerebral Cortex, although it is quick, it also gives you a very coarse rendition. The movements are not refined, it is only after the process get's internalized that you can work on finesse.
Most of this information is based on the National Center of Biotechnology, latest report on this topic, which you can visit at this link.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2553888/
So all in all, it takes about 48 hours to learn how to shoot, with at least 15 or more repetitions at 5 minutes intervals to get somewhere. Unfortunately, due to what I have witnessed, most archers learn poorly everything about archery when they start, and than it takes them years to cleanup their act.
Primarily because, every one wants to shoot a target the first minute they pick up bow, and secondly because, no one spends the first 2 days on concentrating on form, and blank bail. It would also mean a poor business model for any archery club as well
Also, according to Dr. richard A. Schmidt, and Timothy D. Lee, on studies performed on violinists and pianists, they have filtered a statistical average of 300 to 500 total hours in order to learn a new complex skill, and 3000 to 5000 to correct it or unlearn it if need be. Now those numbers are regurgitated by all coaches everywhere, and they have little intrinsic meaning. Therefore I give you the access to the original resources:
http://www.hp-research.com/publication-list
Of course, due to the particularities of each human being, and because no study to date of such extent was performed on archers, we can extrapolate from those researches that:
It is important to have solid planning of your day when you want to change something to your shooting style. Have ample time during the day, with generous brakes in between each set, in order to relearn and consolidate a shooting sequence. Also, plan AT LEAST TWO CONSECUTIVE DAYS TO WORK ON ONE LEMENT. As boring as that may sound. Remember that most numbers shown here and found in any scientific publication are obtained in lab conditions. In a lad, conditions are replicated. So replicate your environment conditions. For instance: if you plan to concentrate on grip over the weekend:
Plan to have 4 hours in both days to do just that. Plan your food, eat the same 2 days. Plan your water intake, drink same amount of water, plan how you train: silent or favorite song in the background. Keep the same playlist. It is good to have an additional stimuli in the learning process. Light (artificial or natural) time. Break down the hours, set and alarm clock, two days at set intervals you shoot and work on that element.
This way, you conserve the total time spent to learn a new element. If you do not pay attention to those variables, you only manage to increase the time you need to master that element.
If you are modifying elements on release, aiming, than make a point to end on a good arrow, on a felt good shot. For at least of couple of days in a row. After that, the learning is consolidated, so you can ad or remove elements, you can become flexible with yourself and your environment.
Keep in mind that you still need to put up at least 100 hours after this initial effort to internalize a new element, and do not sway from doing so.
As a realistic goal, you should look at the magic number of 300 hours, break them down in a year, and consolidate them in pairs of 2 days per shooting element that you want to change. Plan where you want to train, and how.
Training always have 3 elements and now I will talk about the other 2:
1) learning - See all the above
2) shooting endurance - here you need to train progressively, 2, 3, 4, hours, with an interval of 2 days between shooting sessions to allow your muscles to rebuild.
3) mental endurance - focus, mindset. For this you do not need to hit the range. You need to do visualization techniques. This is an imagination exercise, where you should spend the same amount of time as a shooting session, and stare at a target in your office, or wherever, and visualize how you correctly execute each arrow in each X spot, remember the satisfying pop of the paper, bring back the kinesthetic memory of those shots that feel good, and play this imagination game for a full hour or more, up until you complete mentally a full set. 300 on a FITA for example.
It may be hard at first, but it gets better with time.