What's the difference? We're glad you asked!
Planned date: the date that the task appears in your calendar. Click this date to open your calendar to that date!
Start date: the earliest possible date (start-of-day) you can begin working on a task.
Due date: the date (end-of-day) when you would ideally like to have the task completed.
TimeHero uses the Start date and the Due date (among other things) to automatically plan when the task's assignee should work on the task. For example, if you have a 1-hour task "Provide design feedback," which starts November 1 and is due November 7, TimeHero will aim to plan the task on one day between these dates.
If the task assignee isn't available during these dates (e.g. they have no work hours, or have too many other important tasks/events), TimeHero will still schedule the task but after the due date. You'll be able to see this when looking at your project – the task's due date will have an orange-red background indicating that it's behind.