Everything is an emergent property of something. If the universe was extremely dense and homogenous then everything was causally connected...everything happened 'now'. When the universe expanded, space came into being and so did time.
This is my pet idea but the relevance to the OP is that, the Pre-BB mechanism is an open question... as Strange ironically just pointed out.
When thinking aboutthis I think it is important to view everything from the frame of 'inside' the universe, as models that view from the 'outside' just complicates things and may well be in error.