I have time dependent Workflow which send a mail few days before a date field. Even if I change the change the date the scheduling of the workflow does not get changed. It still shows value as per the previous date.
I am using : Evaluate the rule when a record is created, and any time it’s edited to subsequently meet criteria .
Unfortunately, changing the time dependent workflows only affects records that are evaluated following the change. Any records that have already entered the queue for the time dependent workflow are not affected by changes to the workflow criteria.
You can access the queue and manually remove records from the queue. You access it by SETUP -> TIME BASED WORKFLOW under the monitoring section.
Answered a similar question on this matter here.
Does updating a time-based workflow affect the current queue?
Hope this helps