If you have a task list that you would like to reuse, you can easily save it as a template.
1. Click on the task list settings.
2. Select the Save as Template option. You should then see a "Task List Template Saved!" message.
3. The saved task list template will contain the tasks and assignees from the original task list. It will also automatically calculate the task duration in days for the tasks based on the due dates from the original task list and date the task list template was saved as shown below.