I'm using mostly this recipe on OpenBSD 6.0 -current, with a few details pulled in from this other post
https://samuelhewitt.com/blog/2015-0...backups-how-to
I used the Samuel Hewitt version of the share, e.g., "[Time Machine]" instead of "[home]" and a separate user "timemachine" for privsep reasons. And you want netatalk-3.x; the OpenBSD port of it includes avahid support.
BTW, whenever I see a post that tells end users to install 20 compile packages and git clone and the code themselves, I do wonder how that "other" Unix-like system has survived... And I give thanks again for the BSD ports mechanism, specifically, OpenBSD packages. But I digress...