This is relatively simple to implement idea. I have a long trip that starts at the end of month. My trip has several segments and most of them are in the second month. When I want to add items to segment, it asks me if I want to add it to itinerary. When I say yes it presents me with calendar, but calendar is always open at the start of my trip and every time I need to move to the next month. Since you know the segment I selected and you know the date range for this segment you should open calendar for the segment month.