Updating field after due date

I have two custom doctypes, one is the “master” doc and the other one (a maintenance protocol) is linked to it. When I submit the linked doc, I need a way to automatically update the status field of the master doc about 6 months later to trigger a new maintenance visit.

Is there anyway to schedule a server script on specific dates sort of like with notifications?
There are no items or any other details involved. All I need is to change the status field of the master doc 6 months after the linked doc was submitted/created.

Sales invoices “expire” automatically for example. But how do I implement that in a custom DocType?

I figure all I really need is to be able to run a script whenever a notification is sent, how is that done? Can’t seem to find any server script events triggered by notifications.