A protoverse is a universe within its own origin; the "singularity" or infinitesimally small point just before the Big Bang. In particular, it can be used to refer to the point leading up to our own universe.
Protoverses are zero-dimensional. Thus the instant a protoverse "exists", it immediately turns into a Big Bang which like most universal births, creates the universe over a span of billions of years.
Brane collisions create protoverses at their impact point, which then explode outwards into new branes.