Do players need to declare their use of dice from the pool before they roll or can they declare their use if they've failed a roll?
On a side note, can a player make a Lead roll and still roll to contribute to the number of successes to overcome the Threat. I'm a little confused. After all the rulebook says "If there is time..." Wouldn't this mean that the player tries to make a Lead roll, and yet still has time to join the other players to make a dice roll that contributes towards the number of success required to overcome the Threat Level?