I'd say the cosmic or mean astronomical time. Like the Aztecs of ancient times.
In general, the Chinese have their own equivalent of ours (calendar wise), so we could go off of that.
But yeah, there is also that sort of temperal shift or tweak time-space thing. Supposedly reality bends around our atmosphere or ionoshpere? I am referring to an experiment conducted recently how we had 2 ultra precise clocks perfectly synced together, kept one on earth and sent one into space...that one comes back and they are out of sync.
That's all I could think of at any rate.