Almost all the dates in this game have some connection to Lavos.
65 million bc: when Lavos landed
12000 bc: when Lavos punished Zeal's hubris and destroyed their civilization
600 ad: when Magus summoned Lavos to do battle, and was defeated (in the lavos timeline)
1000 ad: not much, but a random NPC mentions earthquakes caused by Lavos.
1999 ad: when Lavos destroyed the world, of course.
2300 ad: The end of Lavos' life-span, and the growth of his spawns.
an important consideration here is the Entity. Robo posits that the gates were created by an Entity that was reliving its memories, sharing its dream with the party, and recruiting them to stop Lavos. Based on this, I would conjecture that the Entity was dying in 2300, it was reflecting on its defeat by Lavos and its impending death, and having flashbacks to the important 'turning-points' in its vast life. I'm not sure of the significance of the present, except that its during the youth of Chrono, Marle, and Lucca, who were chosen by the entity to be its champions against Lavos.
Lavos caused no less than three extinction events. First, his fall wiped out the Reptites. Second, he destroyed Zeal for their impudent act of draining too much of his power. Finally, he destroys the world in 1999, either because civilization has become too powerful, or his biological clock tells him its time to reproduce (and nuke the surface to make it safe for his spawns), or both.
The fact that Lavos destroyed Zeal in particular, and not the Earthbound, is one of the strongest arguments for his intelligence imo. He was aware of the Mammon Machine siphoning off his power, he identified Zeal as the culprit, and destroyed the target that offended him, while allowing a non-magical civilization to develop. This to me proves that Lavos is not a mindless space tick, but an intelligence far above the human race, which he farms as livestock and guinea pigs.
