How do I toggle visibility over time of a sublevel in my current level?

Hey, I was wondering how can I change visibility of a sub level over time in my main level, let me explain myself. I have a level with some objects and a sub level with another ones hidden. When I press a key I can saw the hidden ones but I want them to disapear (unload sub level) over time. Sorry I’m not really good at explaining my self. In my mind it works like this:

When a key pressed the hidden objects become visible for a short period of time, the player can see that on a bar, like a charging bar. They can also pick up some objects to stay in that “mode” for a longer period of time.
I know the logic behind this but I’m not quite sure how to implement it, shloud I use a time table? Or a simple int counter over time? And should I do that on the playerControler or in another blueprint?

Sorry if it’s quite muddy to understand I’ll replay any suggerence, thanks.