This really is important if you have LED signs... Night time gets too bright.

I would add to this that there are 2 ways this could be achieved:

1) Create a transparent black 40%-60% opacity PNG that sits on top of an entire playlist based on a certain time of day. Ideally, you would be able to place an overlay image on top of an entire playlist as a "separate layout" of "overlay layer on top of existing playlist". If you had the overlay layer be flexible, or different playlists could have different overlay layers on top of an existing playlist, then you could actually create multiple different brightnesses for different times of day if you wanted simply by having a different overlay layer on a different playlist based on the schedule.

2) Create a lockable layer inside the layout itself that only appears during certain times and is easy to edit items behind it when the layer is hidden.

3) Actually create a "brightness feature" that puts a transparent black overlay on top of a playlist a different opacity at different times of day (programmed / scheduled opacity on a brightness layer for a monitor?)

Option 2 is not as easy to use for non-technical people, but still could work.

The way we are doing this now is creating duplicate layouts with a transparent PNG on top of them, and then a duplicate playlist referencing all of the duplicate layouts. It's extra work that could definitely be easier to manage.