I don't think we know of anything with the power to cross the timelines.

As I understand it, Alexander's power is to move back and forth through time in a physical space. Alternate timelines may or may not form as a consequence of that time travel, but it is not actually within Alexander's power to do that or navigate the resulting multiple realities.

Meanwhile, Omega has power over the rift that lies between the shards, but whatever separates the timelines is a higher-order divide that would need even greater power to cross, if it's even possible.

I would rather they didn't go down that path, and simply leave it there utterly beyond our reach.