If I create a Approval Workflow I can't add a workflow to a Task Created by the workflow. How could I add a wokflow to a Tasc created by approval workflow.
If you creating Workflow with an Approval you must select which list will be used for Workflow Tasks ( url: /site/WorkflowTasks/AllItems.aspx ). If you want to add another workflow to task, you must create new workflow in Workflow Tasks library for tasks. Make sure you set this workflow Run when Created
you need to update item on which workflow started i.e., On item added one task created so that time updates your new column in an item with task created column and check on it for overdue tasks.
You can use pause event in workflow for waiting for an overdue date for the task.