Captain Seevor ability timing

[Matt Sucharski]

Seevor's jam ability triggers "before attack dice are rolled". Does this happen just before the 'Roll Attack Dice' sub step of the attack process or later in that sub step after the number of attack dice has been determined? This matters against abilities like the TIE Advanced x1's Advanced Targeting Computer. 

[Kris M]

Captain Seevor's (Modified TIE/ln Fighter) pilot ability triggers before Step 2a of an Attack: Roll Attack Dice