What Is the Interaction Between Time Reversal Symmetry and the Standard Model?

So general principles tell you that there's this interaction. And if you sort of put an numerical value to it, you would think the interaction should be like one in appropriate units. But it turns out the experimental limit is more like 10 to the minus 10. So it appears within the context of the standard model to be a coincidence that it's so small. It's not a contradiction with the standard model, but it's something that the standard model does not explain.