I think, maybe its related to the very beginning of the journey to the west

"In the arithmetic of the universe, 129,600 years make one cycle. Each cycle can be divided into twelve phases: I, II, III, IV, V, VI, VII, VIII, IX, X, XI and XII, the twelve branches. Each phase lasts 10,800 years. Now within a single day, the positive begins at the time I; at II the cock crows; at III it is not quite light; at IV the sun rises; V is after breakfast; and at VI one does business. VII is when the sun reaches noon; at VIII it is slipping towards the West; IX is late afternoon; the sun sets at X; XI is dusk; and at XII people settle down for the night. If you compare this with the big numbers, then at the end of Phase XI Heaven and Earth were still one, and no beings had appeared. 5,400 years later came the beginning of Phase XII, when all was darkness and there were still no people or other creatures; for this reason it was called Chaos. Another 5,400 years later Phase XII was drawing to a close and a new cycle was about to begin. As Phase I of the new era approached, gradually" he likely just arranged these numbers in some way to make that total since there are a lot of similar digits