Task must finish 30 days before milestone

I have a milestone and I would like to have a task that must be complete 1 month before the milestone. (i.e. a document is due 1 month before a review.) How can I set this up to have the task dates adjust whenever the milestone shifts?

For my task, I have the following dependent listed: image

I’m not sure if I’ve used the time field correctly, since the task is still just showing up with the defaults. Any help?