There are specific time requirements for each Color Belt Level before being eligible to grade and promote to the next level. The listed requirements are a standard, but in certain circumstances a Sensei may request the student grade sooner or be held off longer from the test. An example may be the student is taking in 4 classes a week then they might be able to test in 6 weeks.

White Belt to Yellow Belt:
8 to 12 weeks, or 36 1 1/2 hour classes, or One 3 month semester

Yellow Belt to Orange Belt:
8 to 12 weeks, or 36 1 1/2 hour classes, or One 3 month semester

Orange Belt to Green Belt:
12 to 16 weeks, or 48 1 1/2 hour classes, or One to Two 3 month semesters

Green Belt to Blue Belt:
16 to 24 weeks, or 72 1 1/2 hour classes, or Two 3 month semesters

Blue Belt to Purple Belt:
24 to 36 weeks, or 108 1 1/2 hour classes, or Three 3 month semesters

Purple Belt to Brown Belt:
24 - 36 weeks, or 108 1 1/2 hour classes, or Three 3 month semesters

Brown Belt to Black Belt:
32 weeks + 48 classes of teaching, or 108 1 1/2 hour classes, or Three 3 month semesters.

Black Belt:
A minimum period of 3 years in Ju Jitsu before being considered for promotion to Black Belt.

There are several reasons for the amount of increased classes once getting to Green Belt. This is the stage where variations are taught and each test you are required to know every single technique from all the previous belt levels. At Green Belt stage the same effort put into a Yellow Belt test would not sufficient for promotion.

Once to Brown level the student should be able to not only perform every single technique in the Goshinkan-Ryu Ju Jitsu curriculum they should be able to teach the technique in a precise manner.