you need to convert into billable units at some point, which is what the fractional system gives you, so it's just a matter of whether or not the UI accepts clock based input or not.

i'm not a UI expert but timekeeping doesn't seem particularly innovative. there are probably all sorts of esoteric certifications and approvals one might need for e.g. DoD compliance, so i'm guessing there are few people thinking about this and fewer willing to get it done and certified for the sake of the users.