It depends but generally, no time is too late until you’ve agreed to a number explicitly. That said depending on how you went about it you can create some bad blood.

Did you discuss comp with them (or through a recruiter) at all?

And above all else, the best time to negotiate comp is BEFORE you start working for the company. Afterwards it is a lot harder to get big jumps in pay.

When looking for a new job when is the best time to negotiate salary? If you receive an offer letter is it too late?