Ki Aikido gradings have two parts, first there is the ki grade and then there is the aikido grade. The ki grades are a test of your ki development. The aikido grades are a test of your aikido techniques. Gradings are structured thus:

You can see that the ki grades and aikido grades almost alternate, you cannot take an aikido grade without having taken the relevant ki grade. The above are minimum time periods assuming you practice twice weekly for about 2 hours each time, in fact even if you practice everyday they are the minimum times. Obviously if you can only practice once a week for an hour or so it could (will) take much longer.