What you should do is remove 1 second per 10 points to remove all 5 seconds should be The value of a tank 10, 20 , 30 ,40 , 50 That should be good or 5 10 15 20 25.
It would be 100 points at 10 points each and or 75 points for 5 increments of time loss. No more 20 seconds only 15.