Reschedule events directly on the calendar
Drag and drop items on the calendar to a new date. The calendar gadget clearly supports it, but there is no hook on the action.
Sorry, this is a bug. Drag and drop in the calendar actually used to work the way you describe. We’re looking into what broke.
In the meantime, you can also drag and drop items between days in the Itinerary list. (Choose “All Days” at the top to see every day in your trip, whether or not it has something scheduled yet.)
Brooke Schlaphoff commented
interactive calendar! to drag and drop items and move dates around etc.