Re: "...using methods that can be replicated anywhere on the planet."
Not true. The speed of light is fixed for all observers. This means that time dilation effects are not detectable to you if you are in the same frame of reference. This means that you will still measure 1 second correctly for your frame of reference using a Cesium clock whether you are in total void or on the surface or the earth or on the event horizon of a black hole.