Some tasks are strongly related to time, while others are not. They should be handled differently from each other for maximum efficiency.
For example, this task is strongly related to time, because you can't do it after the time allocated for it:
- Personal training session with Mr. Muscle.
Other tasks are weakly related to time:
- Email Mr. Muscle to setup next training session.
In the later example, if you miss your allocated time, you can still complete this task. But in the former, you can't show up for an appointment after it's time has passed.
A common tactic I've seen over and over is to create a faux appointment for something which is weakly associated with time. This artificially puts a deadline on the task. This almost never works, as your brain knows whats up. You can't trick yourself.
You're better off keeping a calendar for items that are strongly associated with time and a separate task list for the rest of your "next actions."