During the last supper, at what point did Judas leave? ?

After Jesus had washed the feet of all the apostles, but before instituting a new covenant with them using the unleavened bread and wine. (John 13:2-30)

John’s eyewitness account indicates that Jesus dismissed the traitorous Judas before instituting the Memorial meal. During the Passover, Jesus, knowing that Judas was his betrayer, dipped a morsel of the Passover meal and handed it to Judas, instructing him to leave.

 Mark’s account also intimates this order of events. (Mr 14:12-25) During the Lord’s Evening Meal that followed, Jesus passed the bread and the wine to the 11 remaining apostles, telling them to eat and drink. Afterward he spoke to them as “the ones that have stuck with me in my trials,” a further indication that Judas had been dismissed.​—Lu 22:28.

AS SOON AS JUDAS HAVE DIPPED THE BREAD IN THE DISH HE GOT UP AND LEFT AS YESHUA SAID ' DO WHAT U DO QUICKLY"

John 13:25-30 KJV — John saith unto him, Lord, who will betray you? Jesus answered, He it is, to whom I shall give a sop, when I have dipped it. And when he had dipped the sop, he gave it to Judas Iscariot, the son of Simon. And after the sop Satan entered into him. Then said Jesus unto him, That thou doest, do quickly; he then having received the sop went immediately out: and it was night.

He left just before they brought the check. 

Immediately before the waiter came with the bill...

As soon as Jesus commanded him "What thou doest, Do quickly"  (John 13:27) and Judas "obeyed His commandment" (I John 2:3-5)

When Jesus told him to leave, "What you do, do quickly."