At what point in the three or so years would you say Judas became an unbeliever?
This is around the time when Judas conceived the idea to betray Jesus.
And supper being ended, the devil having already put it into the heart of Judas Iscariot, Simon’s son, to betray Him,
John 13:2
When he acted upon this treacherous idea to betray Jesus, is when his fate was sealed.
JLB