Changing the length of a second would be so insanely difficult that it's probably isn't worth attempting. Pretty mush every other standard unit has the second in there somewhere at some point, so changing that would mean spending decades of changing math on so many things. That story about the Mars probe that slammed into the planet because someone screwed up the units? That would be happening everywhere all the time.

In the end you're always going to have weirdness with time because the orbit of the Earth around the sun isn't going to be divided evenly by the rotation of the Earth. Whatever you do is going to come out janky, so why spend all the time and effort to change from our current jankiness to a different janky system? We'd have to put a lot of time and effort into solving the new problems caused by the new jankiness. Then someone else will probably propose some new janky system to replace that system, and it's a never ending frustration because we'll never have a perfect system because ultimately orbital mechanics don't divide into even numbers.