A.T. Robertson Commentary John 13:30

"He then having received the sop went out straightway: and it was night." — John 13:30 (ASV)

Having received the sop (λαβων το ψωμιον). Second aorist active participle of λαμβανω. Judas knew what Jesus meant, however ignorant the disciples. So he acted "straightway" (ευθυς).

And it was night (ην δε νυξ). Darkness falls suddenly in the orient. Out into the terror and the mystery of this dreadful night (symbol of his devilish work) Judas went.