Change default time of alerts on Mac Calendar app?

Support page says to follow these steps: Change default alert settings in Calendar on Mac. 

But on pull-down menu in all accounts earliest for all day events is 9am. No option to use different or custom time, such a when day starts at 6am. See screen shot below.

I posted this few days ago. No response. Does that mean that contrary to Support page, you in fact cannot change default alert setting?

I know that every time I create an all day calendar event, I can customize change alert time by customizing it to so many hours or minutes before. I’ve done it 100s if not thousands of times. can’t I change the Apple default?

thanks.