If the entire course of evolution were compressed into a single year, the earliest bacteria would appear at the end of March, but we wouldn’t see the first human ancestors until 6 a.m. on December 31.
That’s from Why Evolution is True by Jerry Coyne (which I am reading right now).
P.S. The first organism – simple photosynthetic bacteria – appeared around 3.5 billion years ago, one billion years after the earth was formed. Then about 600 million years ago, worms, jellyfish and sponges (multicelled organisms) came into existence. The first mammals showed up around 250 million years ago, while we humans are newcomers on the scene arising only around 7 million years ago.