Send notification to Assignee Resource as a reminder

Summary:

Send notification to Assignee Resource as a reminder

Content (please ensure you mask any confidential information):

I have created some custom date fields on the case management form which is required by the client. They are also requesting to be reminded maybe a few days before the due date so I was wondering how we could set up a notification for this?

Version (include the version you are using, if applicable):

I also understand there are Tasks and Appointments that I can use but the client are specifically asking to make use of the custom fields. If there is also scripts I can use to set the notifications for the Tasks and appointments I will also be open to making use of this as a workaround? Thanks