So for this, we must understand the concept of Lorentz invariance. Lorentz invariance is the property that it can transform under a Lorentz group. What this means is that it must remain the same under Lorentz transformations to be Lorentz invariant. For a specific time, they will agree on the change in that time under a transformation, $$(t, x) \rightarrow (t' , x')$$