Opacity Tag expression

My English is bad.

I want the hours to be white at night and black at day, but with the option of AM / PM and 24 hours.
If I activate 12H / 24H, I cannot make them appear in a certain period (enabling or disabling the timeline option).
If I program in “timeline” that the black hours appear between 08:00 AM and 06:00 PM, I cannot use 12H / 24H.

So I thought about using the expression tag mode for the day, where at night it was 0% opacity and from 8AM to 6PM at 100% opacity. But I don’t know which expression to use this!
Can someone help me how to create the “expression tag”?

Thank you!

I got it!