How do I create an itinerary with dates attached to stays?

In the Trip Planner, under each stop, you can add the dates you are planning to stay at each particular location.  If you accidentally input overlapping dates, you will get an alert message letting you know to fix the problem. If you accidentally have a gap in your dates, you will also be alerted as long as the stops are consecutive.

For your first and last stops, you should enter a single date (and not a date range).