Question

How many years after the Big Bang did the planets form?

Answer 1

If you are referring to our planets, the ones in our solar system, they formed about 4.6 billion years ago, while the Big Bang was 13.8 billion years ago.

Explanation:

If referring to the planets in our solar system, they formed
`13.8-4.6=9.2` billion years later. But our planets are not the only ones - we have detected many planets in other systems, with the oldest detected planets being around 12.8 billion years old, so they formed about 1 billion years after the big bang.

There are likely even older planets, as yet undiscovered.