I agree that the main bulk of the New Testament was written within a 55 year period. You could stretch it to 90 years with the Gospel of John which was probably written around 90 AD and so is a very late edition. Also there were ad-ons for political reasons. There was rivalry between the Catholics and another Christian sect so the Catholics, in putting the final touches to the New Testament, tweaked it here and there and may even have added to it before presenting it to the people as God's word. Also there were gospels left out of the New Testament because those gospels were not in line with what the early Catholic Church wanted the people to believe.