‘You go up to the Feast. I am not going up to this feast, because my time is not yet fulfilled.' And having said these things to them he remained dwelling in Galilee.'
So He told His brothers to go to the feast, while He remained in Galilee, awaiting God's time. What He, of course, meant was that He was not going up ‘at present' along with the party who are going from Galilee. He knew that He had to await His Father's instructions.
Many good authorities have ‘I am not yet going', and the ‘yet' is certainly to be understood if not there (it is easy to see why it might have been written as a comment and then incorporated into the text). John is hardly likely to have depicted Jesus as deceiving his brothers, and it is clear that He was not yet sure as to what exactly He was going to do. What He therefore meant was that in view of the situation He was still awaiting word from His Father and would not act until then. Once, however, He received that word, He went.
‘My time is not yet fulfilled'. He was aware that danger awaited Him, and that His death would be sought. And He knew that it was not yet time for Him to die. He had a further ministry to be fulfilled which had not yet been fulfilled. So He must wait.