Best way to make countdown with resource bar

I would like to use the resource bar as a visual countdown timer.

From very beginning timer/bar should last 5 seconds - time given to the player to make a decision before next choice appears and resetting the countdown resource bar.

Over the time I want to gradually speed up the countdown resource bar, so player will have less time for decision.

Can you suggest me the best way to to this and to be independent from game frame rate, cuz performance might vary from device to device, therefore result with uneven time.