Again, I don't know the details. I didn't speak much with the fellow to know too much about how his sensei functioned in terms of rank advancement, all I know, based on what he said, was that the sensei tells you when you're going to test and it was because he required patience so for instance if the next belt for you was black belt, even if you were skilled enough for it he might not let you test for it yet because he wants you to be patient. As I said before, I don't see why a reasonable minimum time requirement wouldn't be adequate if you're going to require patience.
If a student has been going to the dojo consistently and they've met the minimum time requirements for their rank I see no reason why they shouldn't be allowed to test for their next rank, including the rank of black belt if that is their next rank. They've shown patience by meeting the time requirement so there would be no reason to hold them back from testing, so in the case of the fellow Im describing above, I see no reason why he would tell students when they're going to test instead of just requiring them to meet the minimum time requirements before they can sign up for their next test.