Trigger a workflow the date of a followup date field

Trigger a workflow the date of a followup date field

Hey all,

can you help us with a custom function, what we need is when a followup date field is created or added a specific workflow related to it should start with all the other trigger sequence and follow the date of the followup date field.
Attached you can see the field and the workflow we want to start on the followup date and not After Rule Trigger Date.\

Best regards.