Hasn't time been proven to not really be a dimension but something we humans created out of thin air?
These "tree falls in the forest" type approaches don't cut much mustard for me. Lots of stuff happened before humans, or any being with the ability to observe, were around.
If your answer is, "Oh yeah? Prove it!" then you would be failing to acknowledge the limitations of observational science, but any physicist, chemist, geologist, etc, would admit that all observational science is perched upon the shoulders of metaphysics (I mean philosophical metaphysics, not spoon-bending tarot card "metaphysics" lol) and not strictly upon observable phenomena. It's more than mere coincidence that the highest educational degree one can achieve in the sciences is a PhD, which is an abbreviation of the Latin for Doctor of Philosophy.
I don't think of time as a "thing" or as something which "exists" in any physical sense (like space itself cannot be observed, but is implied by the existence of an object within it). That's all a dimension really is. It's not something which "exists" in a traditional sense. Rather, it is the background against which other things (objects) exist, and without which those objects could not exist. Time is implied by the existence of phenomena, the continuation of their existence from one moment to the next, and even the coming into being of a first phenomenon (and it therefore precedes that phenomenon).
Fwiw, if you insist on numbering your dimensions, lol, then time would be the first dimension imo, since space continues to exist from moment to moment while time, being a non-physical entity, does not imply the existence of space.
To say that "time began" is a contradiction (as is saying "time ceases to exist"), since a "beginning" implies a time before the occurrence. The same can be said of space (ie, where did space begin?). These neumanal (as opposed to phenomena) entities are therefore infinite by definition. Whether you consider a blank canvas to be a painting, or if it's only a painting as soon as something appears on that canvas, is up to you.