You may also consider the following:
Raise your focus up one level - to the "Outcome" level. At the beginnning of each day (or the night before) select several "Outcomes" that you want to happen that day. These would be the result of the completion of several Next Actions on your "To-Do" List.
You can list these as "Untimed Events" so they appear at the top of your Daily Calendar. If you don't complete them, move them to another day when you think you'll be able to achieve the outcome.
If you have enough control over your day to schedule them as fixed blocks of time, you could always do that too.
Remember - one of David's prime principles is focusing on the successful outcome. The Next Action lists are operating at the lowest level, to make sure nothing slips through the cracks while you're focusing on the higher levels.