Auto Archive Posts by Date, not delete

Hello,
I am looking for a simple way to set a calendar date for a post to auto archive or ‘expire’. I know “Auto Delete Posts” exists but it uses number of days, not calendar dates – despite the description, and of course it deletes. This post and this one asked the same question but didn’t get past the “Auto Delete” Plugin.

The Atropos Plugin lets you use a date, and ‘delete’ or ‘unpublish’ but not archive. If I knew how to change the PHP I would, but cut and paste is my php limit.

I vaguely remember this as part of WP admin, but don’t see it in 2.6.

your help appreciated.

thanks – kurt