Move the time tracking entry box so it sits above the list of people who've tracked time.
Reasons why:
  1. This consistently maintains its position no matter how many people have tracked time on a task.
  2. It's the right visual architecture. You're (I hope) more often clicking on time tracking to track time than to check the details of the time tracked. The thing that's used more should be on top.
This applies to anywhere you can select the time tracking dropdown, so in task view, list view, etc.