This is a timeline of events in the Pokémon world, from my point of view. Data may be incorrect.
day 0: Mew floats around space/time rift.
day 1: Through a vortex, mew lays a egg.
day 2: The egg hatches. Arceus is born.
day 3: Arceus shapes the universe with 1,000 arms. Its shards became the earth plate.
day 5: Arcreus creates the Lake trio.
day 6: Dialga and Palkia create space and time, and the lake trio created spirit.
day 7: The plates are created.
day 8: Now that the universe is created, there was no need for mew to live in the space/time rift, so mew left.