How can you add time to "due date"? Quickly add a task by its due date to calendar in Outlook?

On number 2, you can open Outlook on the Web, open ToDo in the right side bar, then you can drag things from Today or Tasks right onto your calendar at a specific spot. There is not a button to do so automatically. (If you use Planner, you can add a Calendar into Outlook to automatically show tasks assigned to you in Planner with due dates- not what you were asking).