What does it mean Slack is active green dot but with a Z, and how to change it?

I am using the Slack app, and after I touched the computer (a Mac) today, the status changed to a green dot, meaning active, but with a "Z". What does it mean a green dot with a Z, as it seems to mean "active but sleeping", and how do I change it to just active? I clicked on it and can only change it to inactive or active, but not to eliminate the "Z".

This comes from the "Notification schedule" setting in the Notifications menu in Slack Preferences.

Basically, this sets your "working" hours. Outside of these hours, the "Z" will appear to show that you are outside of working hours and your notifications are turned off.

To change this: Slack -> Preferences -> Notifications -> Notification schedule
To change it completely, change it to Everyday from 00:00 to Midnight.