This is what I understand of BB. I will use outside observer to help illustrate. At BB this observer would notice some event, a flash of light and then an infinitely small region, a Point, would plop into existence. (I know photons would NOT be able to actually leave region but i say it anyway for illustration).
At this point, the infinitely small region, Point, is fixed in size to observer and will never change. However, internally, the region develops space, time and structure further this space starts to inflate.
So, now I space/time being mysteriously defined inside this region, which is still infinitely small externally. Space time attributes are unique and do not exist outside of region; observer has no concept of space or time only sees a dimensionless point. Now, since space is defined within this region and then the universe itself defines space, it can not expand into space but rather it's space is growing or expanding. At this point I guess I can say that Space/Time is localize to this region and expanding relative to every point within the region.
Now, if I run the process backwards, the space-time within this region would collapse into super dense stuff; but the outside observer not notice anything different until the space inside the point, or region to us, becomes so dense that it collapses and plops out of existence. At this point observer would think he was seeing things because it would have vanish as quickly as it appeared, if it did at all.
But I guess the stuff our universe, region or point, to observer, persists in is of no consequence since we or any law of classical or QM physics could exist there anyway. Our world and laws are inside this infinitely small but vast point. But still I wish I could somehow how see it anyway.
In second to last paragraph I said space-time collapses because, purely intuitively, I think that Time and Gravity were once unified but somehow broke apart.