Hi Nutman,
In regards to Jesus Earthly Ministry, in My opinion, based on information that won't be cited here, might violate Forum Rules, it was 3 1/2 years. He started His Ministry at the Age of 30 and was 33 1/2 years old when put to death. John the Baptist was born in the Spring approximately 6 Months before Jesus. Jesus was Born in the Month of Ethanim(Sept-Oct) of the year 2 B.C.E. and was Baptized in 29 CE and died in the Spring on Nisan 14 of 33 CE at the Age of 33 1/2. According to Jewish Belief, A Man was fully matured at the Age of 30, hence His Baptism By John and the beginning of Jesus Ministry. Evidence of Four Passovers is found at John. 2:13; 5:1; 6:4 and 13:1. Although John. 5:1 doesn't specifically mention a Passover, but a Festival of the Jews, there's good reason to believe that this refers to a Passover, based on John. 4:35 where Jesus says there's four months before the Harvest. The Harvest season got under way about Passover time. Also, another point to consider is the Prophecy at Daniel 9:24-27 regarding the appearance of the Messiah at the start of the Seventieth week of Years and His Death in the middle of the final week thereby ending the validity of the sacrifices & gift offerings under the Law Covenant.
Anyway, that's My take, don't know about anything else on the matter, Scriptures mentioned above, cited in full below.
Joh 2:13 And the Jews' passover was at hand, and Jesus went up to Jerusalem,
Joh 5:1 After this there was a feast of the Jews; and Jesus went up to Jerusalem.
Joh 6:4 And the passover, a feast of the Jews, was nigh.
Joh 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.
Joh 4:35 Say not ye, There are yet four months, and then cometh harvest? behold, I say unto you, Lift up your eyes, and look on the fields; for they are white already to harvest.
Dan 9:26 And after threescore and two weeks shall Messiah be cut off, but not for himself: and the people of the prince that shall come shall destroy the city and the sanctuary; and the end thereof shall be with a flood, and unto the end of the war desolations are determined.
Dan 9:27 And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate.
Compare the above with Hebrews 9:9-14; 10:1-10. Scriptures Cited Below !
Heb 9:9 Which was a figure for the time then present, in which were offered both gifts and sacrifices, that could not make him that did the service perfect, as pertaining to the conscience;
Heb 9:10 Which stood only in meats and drinks, and divers washings, and carnal ordinances, imposed on them until the time of reformation.
Heb 9:11 But Christ being come an high priest of good things to come, by a greater and more perfect tabernacle, not made with hands, that is to say, not of this building;
Heb 9:12 Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption for us.
Heb 9:13 For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purifying of the flesh:
Heb 9:14 How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God?
Heb 10:1 For the law having a shadow of good things to come, and not the very image of the things, can never with those sacrifices which they offered year by year continually make the comers thereunto perfect.
Heb 10:2 For then would they not have ceased to be offered? because that the worshippers once purged should have had no more conscience of sins.
Heb 10:3 But in those sacrifices there is a remembrance again made of sins every year.
Heb 10:4 For it is not possible that the blood of bulls and of goats should take away sins.
Heb 10:5 Wherefore when he cometh into the world, he saith, Sacrifice and offering thou wouldest not, but a body hast thou prepared me:
Heb 10:6 In burnt offerings and sacrifices for sin thou hast had no pleasure.
Heb 10:7 Then said I, Lo, I come (in the volume of the book it is written of me,) to do thy will, O God.
Heb 10:8 Above when he said, Sacrifice and offering and burnt offerings and offering for sin thou wouldest not, neither hadst pleasure therein; which are offered by the law;
Heb 10:9 Then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second.
Heb 10:10 By the which will we are sanctified through the offering of the body of Jesus Christ once for all.
Hope this Helps You, Samson.