The Universe is revealed as an ever-changing entity, filled with the energy flowing from stars and galaxies. While astronomy covers a diverse range of astrophysical objects and timescales, the emerging field of high time resolution astrophysics (HTRA) focuses on the outermost dynamic limits presented by the Universe. On these extreme timescales, the Universe is still largely unexplored, and the questions posed by this developing field have lead to the beginning of a new scientific quest for answers. The conference “Universe at sub-second timescales” brought together leading astronomers and astrophysicists, who have so far developed HTRA independently, with the goal of reviewing the current state of the art of HTRA, exploring the questions posed, and to discuss where we should go from here.