The great difficulty here is that there isn't one!
Third Degree (3A) is mainly taught for Personal Growth. These Reiki Practitioners are regarded as Ambassadors. They have a comprehensive knowledge and understanding of Reiki and can give the first Reiki "Attunement" or "Initiation". This enables them to introduce people to Reiki and give "booster" Attunements to Reiki Practitioners as well as use the Attunement as a powerful addition to treatments. They are not qualified to teach Reiki.
It is from Third Degree, however that people decide whether to further their trainning as Reiki Masters.
The course is three full days. Selection by interview only.