Enable automatic minor core updates when root of site is a git repository

I have a client site that’s under version control using Git. The single repository is at the WordPress root level, but it is set to ignore everything except for theme and plugin files. I did some research into best practices and found some content on submodules, which I might try next time, but at the moment, I’m wondering if there’s a way to achieve both of the following:

Alter how often WordPress Auto-Updates Plugins

From my understanding of how WordPress updates core and plugins is that every 12 hours it goes out and looks for updates. When does that time get set? 12 hours from initial installation? I ask this because using the plugin auto-update filter add_filter( 'auto_update_plugin' ); you could theoretically only allow plugins to update between certain times but if that certain time does not fall into that 12 hour window then plugins will never be updated.