Did the Precambrian era start 4.5 mya or 4.6 mya

I think you mean billions of years ago (bya) instead of millions of years ago (mya)

The Precambrian time is a huge expanse of Earth's history before the Cambrian period, starting when the Earth first formed 4.5 bya until the cambrian period, 600 mya.

Fun fact: precambrian time occupies 87% of Earth total history

The Precambrian Superera is everything before the Cambrian Period (Paleozoic Era 542 ± 0.6%). It began with the origin of the Earth 4.54 ± 1% billion (with a "b") years age (Gya).