Jacob, I appreciate your time and effort in helping me.

After following your recommendations, I found that the button to enable/disable notifications in SA User Settings became unclickable (while the same 'checkbox' type buttons right next to it were fine). So clearly something odd was going on.

I did some searching in Chrome options and tried a reset to defaults (which also disables extensions). After this, the button became clickable again and I received the popup prompt asking me if I want to allow these push notifications.

Let's see if the timing of those notifications is fixed now... Will report in later today.

So example today: at 4:35 Mountain time (just now), I received about 25 Chrome notifications here on Windows 10 PC. These notifications came out (and showed up on my mobile phone) hours ago. How can I have them show up on my desktop PC as soon as they come out and not hours later?

Yes, 

https://seekingalpha.com:443