Change delay for auto-hide on menu bar
I ran the following Terminal command defaults find Menu Bar and found this:

Found 1 keys in domain 'Apple Global Domain': {
    "_HIHideMenuBar" = 0;
}

The _HIHideMenuBarproperty can be either 0 for Disabled or 1 for Enabled. And that's the same setting found in System Preferences - General - Automatically hide and show the menu bar.

So I guess it isn't possible as of today.