Man's Tradition says Jesus's Preaching Ministry was for 3 years.

Some Theologians say 2 years, and there's those that say 1 year.

Jesus Christ's Preaching Ministry of  "the Kingdom of GOD is at hand", lasted one year. 

John 5:1 After this there was a feast of the Jews; and Jesus went up to Jerusalem.  

The feast of 5:1 is the "Feast of Weeks"

Leviticus 23:15 And ye shall count unto you from the morrow after the sabbath, from the day that ye brought the sheaf of the wave offering; seven sabbaths shall be complete:

Leviticus 23:16 Even unto the morrow after the seventh sabbath shall ye number fifty days; and ye shall offer a new meat offering unto the LORD.

From <https://www.blueletterbible.org/kjv/lev/23/1/ss0/s_113001>

John 6:4 And the passover, a feast of the Jews, was nigh. 

The John 6:4 feast is "The Day of Atonement"

Jesus's Preaching Ministry was for 1Year only.

John calls the "Day of Atonement",   "a passover feast of the Jews,"

John calls it "a passover day" because it's an animal sacrificing day.  It's a day that animals are sacrificed for Sins and Burn Offerings to cover the previous year's sins of the Jewish people. The same sins the people had to confess.

Day of Atonement reference from Leviticus chapter.

Lev 23:26 And the LORD spake unto Moses, saying,

Lev 23:27 Also on the tenth day of this seventh month there shall be a day of atonement: it shall be an holy convocation unto you; and ye shall afflict your souls, and offer an offering made by fire unto the LORD.

Lev23:28 And ye shall do no work in that same day: for it is a day of atonement, to make an atonement for you before the LORD your God.

Lev 23:29 For whatsoever soul it be that shall not be afflicted in that same day, he shall be cut off from among his people.

From <https://www.blueletterbible.org/kjv/lev/23/1/s_113001>

John 7:1 After these things Jesus walked in Galilee: for he would not walk in Jewry, because the Jews sought to kill him.

John 7:2 Now the Jews' feast of tabernacles was at hand.

From <https://www.blueletterbible.org/kjv/jhn/7/1/s_1004001>

 

John 7:37 In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink.

John 7:38 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.

John 7:39 (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)

From <https://www.blueletterbible.org/kjv/jhn/7/1/s_1004001>

John 6:4 And the passover, a feast of the Jews, was nigh.

Comment: Big Clue: the way John worded it: "a feast of the Jews", and the fact there's no "Atonement Day" listed before the "Feast of Tabernacles"

From <https://www.blueletterbible.org/kjv/jhn/6/4/s_1003004>

John 10:22 And it was at Jerusalem the feast of the dedication, and it was winter.

John 10:23 And Jesus walked in the temple in Solomon's porch.

John 10:24 Then came the Jews round about him, and said unto him, How long dost thou make us to doubt? If thou be the Christ, tell us plainly.

From <https://www.blueletterbible.org/kjv/jhn/10/1/s_1007001>

John 11:47 Then gathered the chief priests and the Pharisees a council, and said, What do we? for this man doeth many miracles.

John 11:48 If we let him thus alone, all men will believe on him: and the Romans shall come and take away both our place and nation.

John 11:49 And one of them, named Caiaphas, being the high priest that same year, said unto them, Ye know nothing at all,

John 11:50 Nor consider that it is expedient for us, that one man should die for the people, and that the whole nation perish not.

John 11:51 And this spake he not of himself: but being high priest that year, he prophesied that Jesus should die for that nation;

John 11:53 Then from that day forth they took counsel together for to put him to death.

John 11:55 And the Jews' Passover was nigh at hand: and many went out of the country up to Jerusalem before the Passover, to purify themselves.

John 11:57 Now both the chief priests and the Pharisees had given a commandment, that, if any man knew where he were, he should shew it, that they might take him.

From <https://www.blueletterbible.org/kjv/jhn/11/1/s_1008001>

John 13:1 Now before the feast of the Passover, when Jesus knew that his hour was come that he should depart out of this world unto the Father, having loved his own which were in the world, he loved them unto the end.

From <https://www.blueletterbible.org/kjv/jhn/13/1/s_1010001>