Both scenarios are risky. If you try to negotiate for more in the interview, you're likely to be judged a poor fit for the job. That feels too early for me, you really have to get past the interview stage first. But, the risk of waiting is that you might not get to negotiate with the hiring manager, and you could get stuck dealing with HR for a low offer that won't work.
Waiting, and then asking to discuss the offer with the hiring manager before you decide, is probably the better move. Try your best to sell yourself in the interview, show them that you've got the situation completely under control and you've seen it all before. Then when you get the offer, and it's time to negotiate for more money/responsibilities, show where you can bring more value and why that would be a win/win for the company. Make sure to negotiate with the hiring manager, not HR!