To clarify what’s happening, I think the reason you’re getting “Time down = 0” is because you’re triggering on release, and at that point the key is not held down at all, it’s released, so time down will be 0.
I think the simplest modification to your setup would be to just store “current game time in seconds” when you press down the button, and when you release the button subtract “current game time in seconds” from that saved time.