Well, just to nitpick, seconds do vary in comparative length from reference frame to reference frame...and that actually does start to matter in global computing.
If you want to nitpick, you're going to need to start with Cesium-133 oscillation periods as averaged from over nine billion samples.
This matters when computers are bouncing records about time around satellites and across the global.
Edit: I have no idea what I’m talking about so please do not hesitate to correct me on the particulars!
A bit like complaining that UTC is wrong because it doesn't match your local Solar time.