Der entscheidende Augenblick der menschlichen Entwicklung ist immerwährend. Darum sind die revolutionären geistigen Bewegungen, welche alles Frühere für nichtig erklären, im Recht, denn es ist noch nichts geschehen.
The decisive moment in human evolution is perpetual. That is why the revolutionary spiritual movements that declare all former things worthless are in the right, for nothing has yet happened. [Kaiser/Wilkins]
The decisive moment of human development is continually at hand. This is why those movements of revolutionary thought that declare everything preceding to be an irrelevance are correct -- because as yet nothing has happened. [Hofmann]
The stinger is in the last clause, which seems to deflate everything that comes before it. However, the spirit of the aphorism is plainly in sympathy with revolution, so that deflation doesn't seem to be the intended effect.
I think this is a statement of the messianic point of view; everything is preparatory to the arrival of the judgement, which is not happening yet, but which might happen at any moment. If the decision hasn't come yet, it is not because the moment has been withheld. It is always the right time for the decision. Time never resists or impedes it.
If human error is always impatience, and impatience is understood to mean acting prematurely, then -- assuming that the ideas of one aphorism are meant to carry over into another (and we shouldn't assume that, because it shouldn't be taken for granted that Kafka had a system in mind) -- that would mean human error is the attempt to act decisively, or simply stated, to act. This would mean all human activity is error.
What about animal activity? Many of Kafka's characters are animals, and their activity seems no less erroneous, so it doesn't seem that his choice of animal characters should be considered an escape from error.
If all activity is error, and action is unavoidable, then error is unavoidable. I don't think this is Kafka's meaning.
The real crux of this aphorism is Kafka's affirmation of the idea that the past is not relevant where change is concerned. The moment in which things change is now. What is called the routine operation of things is not change but the circulation of a set of familiar variables from a closed repetory. Change is the appearance of a new variable, and nothing new can arise merely by the extension or rearrangement of the old.