Your right

I don't think it is an illusion. It may be relative and not linear, but it is measurable. there is no concept of speed without an element of time. Almost all physics is useless without time. Even gravity is measure in feet per "second" squared,

Almost how I feel about time. In my brain my earliest memory and what I am doing now exist together, there is no gap between them, temporal or otherwise.

And did you ever notice how you can lay in bed and think and think-thoughts pinging through your mind and 3 hours can go by like nothing? I guess time doesn’t exist in brains.

Now...take a deep breath and revel in the wonder of it all!

Time may be an illusion in some sense, but I'm not sure I see it as making much practical difference. We still exist within that perception. Whether time is a real phenomenon or some sort of emergent property of a larger reality seems immaterial to how I behave. I don't truly believe in permanence of self, with gradual changes from moment to moment transforming me from a person I wouldn't recognize who occupied my relative space 20 years ago to the person I am today. As far as I'm concerned, the only real "me" exists in the moment, replaced by a similar person in the next moment, so gradually as to give the illusion of persistent identity. But if I'm hit by a truck tomorrow, that "me" dies but all the antecedent "me"s are unaffected. The "me" right now is unaffected by a future "me" dying. So, as far as I can tell, whatever is happening with time isn't an issue of a single moment affecting a single entity — "me" — or the far more complex notion of all relative timeframes for everything in the entire universe. If time is entirely illusory, then all I could postulate is that we are in some sense akin to frames of a movie reel (obviously more complicated than that, but metaphorically similar) — where the "me" now is just one frame of the film, and the me in a minute is a very similar frame on the reel, and on and on. So, time might be the entire reel, and from an outside perspective we could see it as a whole, but from where we necessarily reside, within a frame of the reel, we see only the frames that stretch before us and behind us, and that's for us the reality of time. I still have an obligation to those future frames because my actions now influence those frames directly, so I still have to live as though time is real even if it's in fact an illusion.

I don't know about you but if time is an illusion I am going to live as hard as I can in this moment.

If time is an illusion how come we can measure its passage and see its effects?

I think you mean our perception of time is highly subjective. Which is fine for most lifeforms it is.