Reiki level three is the last of three Reiki levels(as per modern reiki training system).
This level is considered to be the master level. You become a Reiki master/teacher after completing this level. Now you can initiate other people to Reiki energy - you create Reiki channels.

Traditionally, it takes a minimum of 2 - 3 years of rigorous practice with Reiki II tools and principles, after which one can be considered for Reiki master level. Many Reiki teachers allow more than 3 to 5 years to pass before considering any of his/her students for mastership.

Greed or Need?
Some reiki teachers are offering crash courses in reiki which allow one to become a reiki 'master' in a week or so. Some are cutting down the duration down to 3 days! Most of the teachers who offer crash courses argue that our planet and its people need healing fast. There are very few healers around and more one can produce healers in a short span of time, the better it will serve the healing needs of the earth.

Traditional reiki purists have a problem with that. They point out that reiki is a spiritual energy. It cant be stuffed into you in a crash course. You have to learn the essence of the energy before applying it, leave alone become a master!!

What i think about the issue? Well, i tend to keep an open mind. While it is true that to learn and master any spiritual discipline ( if we consider reiki as an spiritual energy that is) it takes considerable time, practice and persistence on ones part, it is also true that some people adapt to healing modalities/energies more readily/quickly than others. I can testify to that from my personal experience. Maybe some individuals have better spiritual/physical/mental systems to accomodate any kind of energy, than others. So its really upto the teacher and the student to sit together and find out how much the student is prepared...