Time at the big bang and in very early time after that

[Prins]

Well i read a lot of times the chronological explanation of big bang.
I always wondered what was the shape of time in those early times as we all know time is not definite in itself.
So please explain to me what sort of frame of reference they took for explaining the events according to time and the behavior of time at that times.
Thanks

 

[phinds]

... as we all know time is not definite in itself...

Actually, we DON'T all know that. Time is what a clock measures and it was ticking away at one second per second right after the Big Bang Singularity and has continued to do so ever since.

 

[PeterDonis]

I always wondered what was the shape of time in those early times

What do you mean by "the shape of time"?

please explain to me what sort of frame of reference they took for explaining the events

The standard frame of reference used in cosmology is "comoving" coordinates, the coordinates in which the FLRW metric is expressed.