close tasks automatically

We have built a workflow process for a request in which the tasks are to be done in the future (10to 45 days out) and was wondering if there is a way to specify the date when the tasks are started.

We get requests to perform tasks weeks in advance and the request has many tasks in its workflow, we created the workflow so that the first task is simply a place holder and when it is manually closed the workflow process begins. Currently we look at the due date in the requests and close the dummy task manually which then creates the dependent tasks.

Is there any way to automatically close the dummy task on a specified date? the field can be the request due date or a custom field.

Or is there another way to accomplish this?

Thanks
Sal