[Toadling]

It seems to me that OmniFocus was not really designed for this type of granularity, breaking down a day into arbitrary time segments. I think a calendar application, like iCal or Entourage, might be better suited for such things.

In fact, it could be argued that your use of due dates in this way isn't even a GTD approach. GTD recommends using due dates and scheduling only for things that absolutely must be done at a particular time or they will fail (e.g. doctor appointment, call mother for Mother's Day, pack bags before Friday flight, etc.).

But there are lots of ways to organize and handle your tasks, GTD is only one of many. And not everyone agrees with David Allen. But OmniFocus was designed around GTD principles and works best with that philosophy. That's not to say GTD is the only way to use OmniFocus, but the closer you follow GTD methodologies, the more you'll get from the app.

So, I think your best bet for your plan is still to just create blocks of time, perhaps with alarms, in iCal. Sorry I couldn't be of more help.