Posts not being set to draft

I am using the Post Expirator on a website where we are using Postie (https://www.ads-software.com/plugins/postie/) to automatically post alerts that arrive by email. I would like for these alerts to be changed from published to draft 8 hours after they are published. So far, I’ve been unable to make Post Expirator work as expected. Postie is publishing the posts, but when published, the expiration time is not being set.

I placed the following in the Custom field in the settings screen – +8 hours – should I have included anything else in that field? Maybe the quotes (“) at the beginning and end of that information? Anything else?

Any help is greatly apprecaited.

https://www.ads-software.com/plugins/post-expirator/