Since all things we know have a beginning and an end, we can also assume that time itself has a beginning and thus was itself created. All things that are created have a beginning - an inception or manifestation - and thus their time of existence can be measured. Theists believe that God is the creator of all, and this includes time (God being the creator of time): beginnings, inceptions, manifestations, etc.
If God is the creator of time, he exists outside of it and therefore has no beginning or no end. All that God has created has the trademark of the creator: life itself; all that has a beginning and an end.
1. Everything that begins to exist has cause of its existence.
2. The universe began to exist.
3. Therefore, the universe has a cause of its existence.
a. From nothing, nothing comes.
b. Therefore, if nothing existed in the past, nothing would exist now.
c. Whatever begins to exist has a cause of its existence.
d. If the universe began to exist, then the universe has a cause of its existence.
e. The universe began to exist.
f. Therefore, the universe has a cause of its existence.
g. An actual infinity cannot exist.
h. An infinite regress of cause and effect would be an actual infinity.
i. Therefore, something must always have existed that is the cause of all other things.
But how was "time" created?
"Time" is simply what human-kind describes as the start and end of things. Things close to the end of their existence are usually considered "old", and things close to the beginning of their existence are usually considered "young". While the measurement - e.g. how fast, slow, young, old, high, low, etc. - is man-made, the concept of time existed long before we gave it a name.
We, mankind, learned that there was an order to things in their lives and in the universe, but what created that order? That sequence? Those beginnings and those ends?
If we talk about space, time and the universe: Nothing can have an end if it doesn't have a beginning. Conversely, nothing could have a beginning if it didn't have an end.