We looked at the numbers and it's actually a very, very small percentage of applications that run between 18 and 24 hrs per day.
Eighteen hours a day is enough to keep your app running from 9AM to 3AM every day, and unless your application has a global reach, it should naturally equilibrate into a comfortable place.
We are asking that if you want 24x7 wake-time that you pay for a hobby dyno, but if you can let your application sleep when you do, you won't see any difference at all.
There's a huge difference between 24 hours/day and 18 hours/day, but I don't think there's such a big difference going from 18->12, so I don't think many people will care about this improvement.