So, when I use Krennic command card that gives a unit a free standby token can I then use the standby token. Then later when I activate that unit shoot again since I didnt "perform" an attack action I used a standby action.

Yes. The 1 attack per, is only during the activation. If you were able to use your standby, then activate the unit later in the turn, you could shoot with it as you please.