How to change when standing hours starts

Hello everyone. Been a Fitbit user for a decade. But their constantly failing products and horrible support has finally gotten me and the rest of my family over to the apple watch.

We have an apple watch 6 GPS.

How do I change what time the standing hours begin? Right now it starts at 6am. I know I can change how many hours but I can't find anywhere to change where it starts. Don't know why it starts at 6am when I have the sleep set until 8am.

Thank you.