spacetime - Where in, Einstein’s "On the Electrodynamics of Moving Bodies" (Relativity), is “Time” reasonably shown to exist, or why is it a valid assumption?

Given the widespread acceptance that “Einstein’s Relativity” reasonably proves the existence of Space-‘Time’, and thus “Time”... Can any member of the Physics StackExchange please show precisely where, in "On the Electrodynamics of Moving Bodies", (or related core Relativity) papers, “Time” is actually, in any reasonable way shown to exist, as opposed to just, or only being (unscientifically) “assumed”? (added) or, why it is legitimate for the paper to make this assumption or axiom?

Many individuals and publications refer to Relativity as our best theory of Space, and “Time”, and thus imply it is a given that time exists... because Relativity intricately employs the concept of time.

But wherever such claims are made, they are rarely accompanied by any clear justification or specific reference to a specific section of SR or GR. At best, it is claimed that SR proves “Time dilation”, and thus the existence of “time” as a genuine dimension.

Therefore unless it can be shown that Relativity, ("On the Electrodynamics of Moving Bodies" etc), actually incorporates a reasonable proof of times existence, or cites such a proof, or even just gives a valid reason to “suspect” a thing called “time” might exist, then the “time dilation” shown may in fact prove only that moving things “are” changing “slower” (i.e just at a dilated rate), than stationary things, and not that a “temporal past”, and/or “temporal future”, or thing called “time” also exists. (As per space-“time”, block-“time”, growing block-“time” etc).

Precisely where Relativity is valid in assuming a thing called time exists, is a very important question, given the large number of theories based on the belief Relativity does proves time’s existence. And, the large number of fundamentally conflicting theories about time, problems resolving quantum and classical “time”, and even disagreement about time’s actual existence or not.

Therefore, if anyone here on the stack exchange can show just where "on the electrodynamics of moving bodies" actually, legitimately validates its use of "time", or why they accept its assumptions in the specific area of "Time", please clarify this not just for me, but I assume many others..