Hours + Days = DOLLAR$$$$..." Hi-Ho, Hi-Ho, to the McDojo I go...."
Rank should be awarded upon skill, not minimum requirements.
Train as if you are going to die, not tumbling around in your pajamas at a slumber party!
I agree with grading according to skill. I've seen people who have had the days fail because of skill. And I don't like the mentality that you should be given a belt just because your days are up. Frankly, it takes most people more than 600 days to be good enough to meet the standards of Nidan.
But I disagree that keeping track of how long you've done something is useless and just for money. I see where it has its place in correlation to a student's development. It is generally accurate. It does take about 60 days or more of training for most people to be able to pull off a 5th kyu exam.(according to the standards set by this particular federation.) And it does generally take 700 days or more after nidan for a person to be able to perform up to the high standards of a sandan exam.
Hombu dojo goes by days as well for this reason.