What is the nature of time?

I would say time is the category within which space and matter and energy function. I don't think God will created 16 billions years in six days. Why would would God fool us by creating 16 billion years in 6 days. He could as well have created us in 16 billion years days. Some people say that God created us in six days. I think that is not true, unless that 'six' days is in figurative sense. How could the plant be watered and be made to grow in a day or two, and how could the light of the star reach the earth so early? One can say God can miraculously do all those things. Did God create Eve after 5 hours of creating Adam. And then when did Adam feel lonely? When did he sleep? Immediately after creation? There are all sorts of problem if we read the Genesis too literally. To say that God takes long time to create the universe is not at all wrong, as far as I am concerned. The word 'day' (Yom in Hebrew) need not always be translated as 24 hour duration. It could go both ways, 24 hr duration as well as long unspecified time.

Time is the universe.

You may be very much right in your opinion. Time is very much relative. In one frame of reference it may be more while in the other is very less. Therefore all the scriptures may be right in their opinion.