Since Our Lady didn't give us a specific timeframe for when her Immaculate Heart will triumph, we can only speculate - but I think it makes sense to look for the Triumph of the Immaculate Heart around 2029, 100 years after the request for the consecration.
Here's why.
The director of the Association of Marian Helpers, Fr. Chris Alar, MIC, opened my eyes to a key piece of information. Relying on the information in Fatima for Today, by Fr. Andrew Apostoli, CFR, our timeline at marian.org/Fatima relates:
Aug. 29, 1931: In Rianjo, Spain, our Lord communicated to Sr. Lucia His dissatisfaction with the failure of the popes and Catholic bishops to obey His command to consecrate Russia. Sister Lucia also recorded our Lord later saying: "They did not wish to heed My request. Like the King of France, they will repent and do it, but it will be late. Russia will have already spread her errors throughout the world, provoking wars, and persecutions against the Church; the Holy Father will have much to suffer." Our Lord is referring to His Sacred Heart apparitions. On June 17, 1689, the Sacred Heart of Jesus manifested to St. Margaret Mary Alacoque. As relayed by St. Margaret Mary, Jesus commanded the king of France to consecrate France to the Sacred Heart. For 100 years, the kings of France did not obey. On June 17, 1789, King Louis XVI of France was stripped of his legislative authority in the course of the upheaval that came to be known as the French Revolution. This same 100 years was the time of the so-called "Enlightenment," when humanity sought to privilege reason over revelation. For more on the consequences of the late consecration of Russia, see "Has Our Lady's call for the consecration of Russia to the Immaculate Heart been answered?"
So if the fulfillment of Fatima will be as it was with the King of France, it would make sense for the crucial time period to be 100 years from the request for the consecration.
The request wasn't made in 1917. In the secret of Fatima, we weren't even told how to answer Our Lady's requests, only that she "will come to ask for" the consecration of Russia and the First Saturdays of Reparation. Our Lady then proceeded to make her request for the First Saturdays in 1925 and her request for the consecration in 1929, explaining the requirements for each.
However, the 1917 secret does make clear that our responsiveness to her requests has affected and will affect when the Triumph takes place. Maybe we could see the Triumph very soon if enough folks were faithful to the Five First Saturdays, the daily Rosary for peace in the world, and devotion to her Immaculate Heart alongside the Sacred Heart. Given that St. Joseph appeared at the Oct. 13 apparition, consecration to St. Joseph and the Year of St. Joseph gives me hope.
I must repeat: Any specific date or timeframe is speculation, but we do know what's been given to us by Our Lady of Fatima as the remedies for the evils of the age. The more we use those remedies and promote them, the better it will be for the Church and the world.