Suggestion: Realtime/time and date based transitions

Sorry if this has been up before.

*Suggestion:*

Ability to set a  real-time based start and end for a transition/CSS at a
certain time during the day.
And even date.

*Example: *

Clock and/or even Date values could be set to trigger a transition.

*Why:*

This would allow users to have time based website designs.

At night a website could change to a dark theme.
Adult type content and ads containing violince etc could be displayed only
after a certain time.
You could make a CSS clock by timing the transition to a real clock.

Opening hours of events could be displayed.

/Gabriel