"Late" or "too late" is offset by Our Lady's consistent message that "In the end, My Immaculate Heart will Triumph." I think late/too late relates to Her other temporal warnings - i.e. the world will be infected by communism, the good will be martyred, etc. In other words, Fatima offered the world peace if Russia was consecrated. If such is delayed, then there will be consequences. "Too late" means, in my opinion, too late to avoid suffering, heartache, and agony, which could've been avoided if the Pope had done the consecration 90 years ago, back in the 1930s.
Similar to a person who puts off their conversion of life until they are old. Assuming God grants them such graces, they can still get to heaven but they are going to suffer in Purgatory a LOT longer than if they had straightened their life out when young.