How does Github save time over the predecessors like self hosted a Git or SVN repository?
Github is, primarily, managed source code hosting- but it has more components, so lets break them out:
1: Source code hosting
2: Web view
3: Issue tracking
4: Project management tracking
5: Search
6: Authentication and identity (oauth2 and "applications")
7: Documentation rendering
8: Web hosting (a-la github pages)
9: CI pipeline (github actions)
SVN replaces point 1, and poorly. How many hours do you need to manage an SVN server? Very few I would wager but it at least behooves to ask the question. And it certainly behooves to understand that you're not replacing 1:1; you're replacing many things with one, and managing the above yourself can be done cheaper, but poorer, so that "poor" imitation could cost more time for using it too.
It's a very nuanced topic but an interesting one, and reductionist questions like this are not helpful.
If you averaged the time out, it may not have hit the five hour per week mark, but it combined with other time savers (linking Git directly with the issue tracker for example instead of having to figure out how to cross reference them) easily did/does.
The claim was 5 hours per employee per week. I found that it took far less than 50 hours a week when working at a 10 person company. And if it did, I'd question the competence of whoever was doing that maintenance.
I'd pin it at closer to 3 or 4 minutes per employee per week, with maybe 8 hours of setup once. That's still a bunch of work, but it's a whole different ballgame.