Inactive project deletion

I am looking to find out more information on the inactive project deletion feature.

I want to enable this on our self-managed instance but have some questions beyond the information available in the documentation.

Let’s say I want to delete all projects that have been inactive for 12 months. with an e-mail warning at 11 months.

If I enable inactive project deletion with the above settings, what happens to all the projects that are already inactive for 12 months or more? will they be deleted immediately without warning the user?

I want to avoid this, so can I set deletion to 0 months and set the warning to 11 first? leave it a month and then change the 0 to 12 on deletion?

Would appreciate some advice! Many thanks.