Get Everything Done

What is the best way to define the daily workload? I'd like to think when you have worked on every goal enough to make sure it will be reached. The problem with that is, you can never know that.

Well, you can say, work as much as possible, but that leads to burn-out. How would that increase the chance of success?

In DIT there is this mechanic of saying that after the Closed List is cleared, further work becomes optional. That fails to address the amount of work you would do on each individual task however.

The only thing I have at my disposal is setting a stopping time and trying to work as much or as best as possible until then. Any other solutions?