How many hours of meditation do I need before I can consider myself and expert?
How Fast Can I Learn?
Matajuro journeyed to the Kumano shrine in the province of Kii, where he had heard of a great teacher called Banzo. The monks at the shrine told him that Banzo lived as a hermit in the nearby mountains, and showed him the trail to follow. Eventually he found Banzo asked to be accepted as a student."How long will it take me to learn swordsmanship?" he asked. "The rest of your life," was the reply. "I can't wait that long. I will accept any hardship, and will devote myself completely to the study of swordsmanship." "In that case, ten years." "What if I train twice as hard?" tried Matajuro. "In that case, thirty years." "Why is that? First you say ten then thirty years. I will do anything to learn, but I don't have that much time." "In that case, seventy years."
Sensing the direction of the conversation, Matajuro capitulated and agreed to work as long as it took, and do anything he was told. However, for the first year all Banzo had Matajuro do was to perform simple physical tasks such as chopping wood. After a year of this Matajuro was disappointed and demanded that Banzo teach him some swordsmanship. Banzo merely insisted that he chop wood. Matajuro went to the woodpile and was chopping, but inwardly he was furious. He resolved to leave Banzo the next day. But while he was chopping Banzo crept up behind him and struck him painfully with a wooden sword. "You want to learn swordsmanship, but you can't even dodge a stick," he said.From that day on Banzo would creep up on Matajuro and attack him with a wooden sword.
Eventually Matajuro's senses became heightened, and Banzo had to change tactics. Now Banzo would attack repeatedly, even when Matajuro was asleep. For the next four years Matajuro had not a moment's rest from the fear of unexpected attack. One day, when Matajuro was stirring some food on the fire, Banzo crept up and attacked him by surprise. Without thinking Matajuro fended off the blow with the lid of the pot without taking his mind off stirring the food. That night Banzo wrote out a certificate of mastery for Matajuro. --Michael Stone
As some people around here are giving "straight" answers, I will gild the lily above with some comments.
Mastering an art for oneself is very different than learning how to teach that to others. Very often, people look to someone of recognized mastery at practice and teaching to "authenticate" or "recognize" the mastery of the learner. This is because people love to deceive themselves about their own competence both in excessively aggrandizing themselves or not recognizing their own strengths.
That said, the teacher you choose determines the nature of the skill and practice you will acquire. This is why we look to even more people to evaluate the esteem that the teacher we might follow has accumulated. But, in fact, this is just listening to rumors.. one must appreciate this.
Meditations come in two basic flavors.
Mindfulness Meditation - that creates the space to respond most appropriately to current perception by examining and shutting down all background thought loops (rumination, agitations, fascinations). The process is pretty simple.
You sit, try to focus on something (your breath, a sound, some non-sense word) which you can't do because your mind keeps looping through your thoughts, cares and concerns, but the boredom of this loop eventually dawns on the mind as it repeats endlessly.
This looping is not useless, it is how the mind encodes data and keeps short term memories fresh for action. However, this facility is a dual edged sword and our rumination can make us insensitive or unresponsive to our current reality and thus exposed to making dangerous misjudgments.
The quiet or non-informational focal point is a touch stone to practice this letting go, over and over until it becomes second nature. Thus, these obsessions are let to rest and you are better able to focus on your breath or how you legs ache. This is why this practice is best done in a quiet place with few distractions, as distractions defeat the purpose. Nevertheless, mastery of this form of meditations is often noted by being able to settle down into it in the midst of any situation and concentrate fully with your whole spirit on the task at hand.
Prayer or Meaning Meditation - This style of meditation focuses on an object of meaning or information. The "Rosary" in its repetitions is not a carrier of meaning thus is more of a mindfulness meditation, with a slight meaning load. Rather, prayers such as said before and after meals, at church or in daily devotionals are of this sort, but only when they are repeated numerous times whether in a single session or over a period of time such as days, weeks, or years.
Meaning Meditations such as a Shabbat or Sunday prayer service have very similar neurobiological effects on the human system in the way of endorphin release and this is a widely overlooked key benefit of weekly church attendance.
But, in a deeper sense, PRAYER IS PROGRAMMING. Do not make the mistake of assuming that your brain isn't absorbing and modifying its "goals" and "values" as a result of the prayers you pray. In fact, repetitions of prayer have essentially the same impact as "hypnotic" suggestion because essentially they operate via the same mechanism. Be careful of what you are praying, because what you are praying, you are becoming.
This is true in a secular or religious context. People think that just because they are not kneeling in a sacred space, that they aren't praying. But, repetition of choices, visions, ideals, slogans in a sincere concentration is all that is necessary to jam these sort of suggestions into the "rule" processing stack we use for decision making.
The expertise of how to craft and teach prayers that modify people's behavior for their benefit rather than your own is a huge challenge. This is why sources of "NEW" texts are subjected to extreme scrutiny. This is why many are suspicious of the existing sacred texts.
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Meditation is a technique that is in service of some greater organizing frame. It is this organizing frame and the meta-rule formations that surround it that often presents the largest challenge to the mastery of any meditation system.
Given all of this, be extremely wary of the impulse to declare yourself having expertise in this practice. As many suggest in the other answers, it is good enough to just struggle to use the technique and enjoy its benefits. The call to teach will come in due time, if at all.