But these settings don’t seem to have an effect, even if I close Preferences, close the app, and reopen the app. (Also these settings are not documented in the preferences.html document)
The preferences settings change the shortcuts, not the intervals. You can change the intervals of new cards from the “Learning Steps” option in the deck options screen. I recommend reading this too to clear any confusions about how intervals work: Anki's not showing me all my cards! - Frequently Asked Questions