My understanding is that’s exactly the point. To make clocks on the Moon be synchronized with UTC and not drift over time. You can only do that by making the clocks physically tick at different rate. This is because of relativity - time itself on the Moon passes at slightly different rate than on Earth, so if your clock is precise enough, you need to compensate for it. Just like GPS satellites need to compensate for being in slightly lower gravity and going fast relative to stationary clocks on Earth’s surface. This isn’t any kind of illusion, this is how the universe really works. If you’ve seen the movie Interstellar, it’s basically the same effect they experienced on the planet orbiting a black hole, just a much less extreme case.