It is currently possible to set relative start and due dates for subtasks created through a triggered rule
It is not possible to set a date X days before the due date. While it is possible to specify X days after the start date, that does not enable the ability to automatically set due dates of subtasks to a certain number of days before the due date if task durations are not always the same.
If I know a task always takes 5 days, then I can use “task due in  days based on start date of trigger task” and create subtasks (I use it for review) that are due the day before the trigger task is due.
This rule doesn’t work if the duration is different. I’d love to be able to set the due date as “due in [-1] day based on due date of trigger” as this would allow an automation that works for production tasks of various lengths.