Should I negotiate salary during interview or after job offer?

Hello, I am a recent grad applying for a entry level position. I don't have much interview experience so I would like to ask for advice.

I had my 1st interview and I asked about the salary range. He told me that salary is usually discussed in the 2nd interview but he told me anyway, which was around 40-50k. Now they want me back for the 2nd interview. Obviously we'll talk more about the salary then, but should I negotiate during this 2nd interview? I want to ask for the highest end of the range which is 50k and I know that I have the requirements they are looking for. Or should I wait until I actually get the job offer? Thanks.

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