If you post your messages only to your own relay then in theory you could delete them after a couple of weeks the way you wanted. But they'd only delete from your own relay, if they were boosted onto other relays they wouldn't be deleted from there.

Possible you'd be reducing discoverability a lot posting only to your own private little relay.

I think the culture here is more to post to multiple relays for redundancy rather than bother to run your own. They're just dumb drop-boxes. If you post to half a dozen on them anyway having another that you run yourself doesn't seem to add much.

Glad you're liking Umbrel.