The time travel conundrum in babylon 5 is wrapped around the triluminary device and the central character of Sinclair/Valen. The time loop that we see, spanning over a thousand years whereby Sinclair becomes Valen, travels back in time via Babylon 4, and becomes a catalyst that changes everything. There is a massive timeline change, seemingly orchestrated by the Vorlons, who are seen to accompany Valen on meeting the more primitive Minbari civilization.
This means that the original timeline sequence, where Valen and Babylon 4 never appeared back in time, was where the last great war between light and dark forces ended with the Shadow forces defeated but still largely intact. The consequence of which is that in the subsequent war between light and dark, the Shadows prevail. It seems that only the Vorlons and their allies possess this time travel technology, so that they must have devised a way of “cheating,” and going back in time to win the war. Although it is never mentioned in Babylon 5, it must a very different universe without the Vorlon created time loop; the Minbari civilization without the influence of Valen, and the changes that resulted. Somehow, in this postulated timeline, the Vorlons must have used the triluminaries to change a Sinclair, whose life experience is totatlly different than that observed in the series. He is trained and instructed to be Valen, and be a catalyst to radically alter the timeline and establish a stable time loop. There is probably no Earth-minbari war in this original time line.
original time line; vorlon send a Sinclair version one, back in time to be Valen version one , catalyst to alter Minbar civilization, create caste system etc. The triluminaries used to alter Sinclair to Valen are sent back in time without a Babylon 4, and become holy artifacts in Minbari culture.
The result of Valen version one, being introduced to alter the timeline is that the new timeline is closer to what we see in the series but where Shadows get defeated in the last great war but with a great deal of their forces intact. A new Sinclair version two, is born and grows up being much like the one seen in the series. The earth minbari war occurs and the a triluminary is used to determine that Sinclair version two, has the “soul of Valen” or Dna of Valen or something along those lines and the war ends, and the humans avoid being exterminated by the Minbari. This triluminary is the same as that which created Valen version one, as it got sent back in time in the first place, same as the one which alters Delenn.
However, in the new timeline, the origin of the triluminaries is epsilon 3. In fact, there are two sets (used future set in Minbari possession and unused set from epsilon3) of the three triluminaries for an unknown period of time, possibly a thousand years, much like there were two sets of Sinclairs version two, during the episode where Babylon 4 is stolen in the time loop. The original set of triluminaries are used to alter Sinclair version 2 into Valen version 2. These triluminaries are sent back with Babylon 4 with Valen version two, to become the set that the Minbari had in the series, for the past thousand years. Valen version two replaces valen version one due to the time loop. Because Valen version one and Valen version two do not share the same life experience, their actions and influence will probably differ and alter the timeline each time more and more subtely each time the loop is played. Finally leading to a stable timeline after the time loop sequence.
In conclusion, the Vorlons are cheaters of fate, by using time machine to alter the timeline, for the win!