Currently when importing start and due dates from CSV into Asana (and Asana date formatting in general) - you can have a defined start date and end date as to separate columns or you can important them so they consolidate into one ‘start date’ column.
The calendar view only displays the due date for tasks with a start and due date. It will show the task across multiple days if it has a ‘due date’ 1/1/2024-1/7/2024. This gives the appearance that they due date is across multiple days.
There should be the option to show in the calendar start date and end date, or to show due date range - or both.
I use start dates to manage work done and know when to follow up. The wrong time to follow up is once it is already in the time frame to be due.