If the universe really began at zero time, then is the infinity theory already disregarded

if time began at zero then (PI) 3.1415.... which is a basis of infinity does not exists. In which i think is a contradicting philosophy.

The infinite-in-time, or Steady State Theory was discredited years ago. It does not match any of the observations we make. We must, however, qualify that statement. In THIS Universe, time did indeed start about 13.7 billion years ago, along with all of the space in it. However, there are many theories that suggest very strongly that what we call "everything" isn't really "everything" at all, but just one among who knows how many other everythings contained in a sort of super-universe. The most promising of these theories to many physicists and cosmologists including myself is called M Theory, and I recommend you check out the Wiki article on it. What happens to time in that Multiverse, we have no way of knowing, though there it probably is infinite forwards and backwards. In our Universe, as soon as infinities appear in our equations we run screaming because that always means the formula is wrong somewhere, and even if much of it is right, can only be an approximation.

Well, I'm really not into cosmology and philosophy, but the way I see it, if the universe did have a defined moment of beginning, a time stated as the beginning of time, then it's completely fine for the universe to exist for infinity time into the future.

If infinity theory is what you say it is, and the universe did have a defined moment of beginning, then yes, current infinity theory is wrong. And if so, then it doesn't need to be disregarded. It just needs to be revised.

I don't understand why you're so hooked on infinity referring to forever in both directions. You can certainly have the interval [0, ∞). The set of integers is still infinite, but it only goes in one direction.

Time is nothing in itself. The unit of time is 1/365*24*60 of earths movement round the sun measured in comparation movement of the pendulum of an old fashioned watch or some other movement or process.

We might start at the big bang, but our journey around the sun started a long time after this happening, if it was that way. My be we discover some facts that prove theory of big bang to be untrue.

time is when we say it is. it is arbitrary. so is zero time. also, bringing Einstein into it, it is elastic. 'Zero time' is just an arbitrary reference point.

π is not a basis of infinity. Philosophy is more than just saying thing that confuse you.

Time and the value of Pi have nothing to do with each other.