NSTimer slowing down and pausing when minimized

Question

I've searched endlessly for this answer and am surprised I haven't found anything (yet).

What I have is an app with a super simple timer function; start the clock timer, and seconds start to click up. If the app is in the foreground, the timer fires every second and then updates the UI accordingly.

If I minimize it or it goes into the background, then after about 30 seconds or so... the selector action only fires every 10 to 20 seconds... I haven't sat and tested how long the intervals get, but it clearly is more than 1 second.

I've simplified the code below to scrape out all the unnecessary U.I. .stringValue calls better readability. So here's what I've got:

@property (assign) int seconds;

@interface ViewController : NSViewController {
    NSTimer *myTimer;
    bool timerRunning;
}

-(void)btnAction { 
    myTimer = [NSTimer
                  scheduledTimerWithTimeInterval: 1.0
                  target: self
                  selector: @selector(timerAction)
                  userInfo: nil
                  repeats: YES];
}

-(void)timerAction {
    _seconds++;
    NSLog(@"seconds: %d", _seconds);
}

I've also toyed with GCD a bit with this:

dispatch_async(dispatch_get_main_queue(), ^{
     myTimer = [NSTimer
                  scheduledTimerWithTimeInterval: 1.0
                  target: self
                  selector: @selector(timerAction)
                  userInfo: nil
                  repeats: YES];
});

But ended up with the same results.

Lastly... I have a similar (albeit different) app on iOS that had similar issues that was solved after I added this to the AppDelegate:

[[UIApplication sharedApplication]
setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];

I've looked for something similar in the macOS world but to no avail.

So... hit me -- what the heck am I doing wrong here?!?