scheduler workflow state change

Hello to all.
I need this
I have a type of content (events) in which there is a field cck Dates (with dates start - end dates).
I would like to schedule a change of workflow state (of expired) for all the content-type events by end dates.

How can I do?
PS
There would also be considered that the field cck dates also provides the only entry of start dates, so at this point (only if you give end is empty) the reasoning of the scheduler should be based on the start date and end.

Thanks