For those that didn’t take physics classes, or forgot.
In short, and oversimplified, the closer you are to a gravity source, the slower time passes for you.
The moon’s location at X distance from center of the earth, versus the distance from the surface of the earth to the center of the earth, is enough to be quickly noticeable.
Fun fact, I believe that GPS satellites must also account for this (given that they are just fancy time measuring triangulation machines) and they are extremely close to the center of the earth, compared to the moon.