Help with sliders

In my game, I want a have a timer that counts down from a value stored in a variable. I then want a slider to visually show this change. however, I don’t want the slider to go down as the timer goes down, I want the slider to fill up as the seconds left reaches 0.
The reason I want to do this is that I want to have a button that updates text but only after the timer reaches zero. I am unsure about how to get this to work. Any help would be appreciated.

Configure the slider like this.

  1. Set Minimum Value to 0

  2. Set Maximum Value to the value that you are counting down from

  3. Set Value to (The value that you are counting down from - Current count down)

  4. Update Value in Step 3 whenever current count down value changes

This would fill up the slider instead of emptying it when the count down goes to 0.