From 55 to 52 million years ago is when the Pakicetus lived intill evolution erased it.
From 50 million to 47 million years ago lived the Ambulocetus intill evolution erased it.
Around 45 million years ago the Rodhocetus lived intill evolution erased it.
Around 40 million years ago the Dorudon lived intill evolution erased it.
In this time period whales evolved into the basic whales that we know today.
These are basically the baleen whales that we see to this day and haven't changed much since they first lived through evolution 35 million years ago.
These whales have lived since 30 million years ago and have remained basically the same to this day.