Good idea for a work around but unfortunately the the task does not show up in the My Day view in the calendar to do bar (even though it does show up in the To Do app). It seems like Planner tasks will not show up in the web to do bar at all.
It is a real pity because the work flow of having a centralised place for tasks either added manually, flagged emails, or assigned tasks from Planner, then dragging tasks to the calendar to allocate time to work on them is great. But if you don't have the centralised pool of tasks to draw from, it loses its appeal very fast.