We have regular gradings every four months for Kyu grades. There is a list put up on the notice board where you put your name and the grade that you will be taking. The instructors keep a log with the actual "mat hours" that you have put in. There are minimum time requirements that are posted but those that do just the bare minimum are less likely to shine at grading time. If you have been intermittent in your training or if you have blasted in the minimum hours in the last few weeks before grading you can be asked not to take it(that's happened to me). For Dan grades you are invited. The Dan gradings are held once a year in September and the whole thing is a big event. Further than Shodan is purely by invitation.