You can post-IPO - depending on liquidity. I don't think that'll be an issue here.

And if the thesis of "it's going to look good for the first 15 days" holds, you can indeed be very profitable by e.g. buying ATM puts. (The problem being that markets don't like sticking to time tables just to accommodate your investment thesis ;)

So yes, you'll be able to take a bearish position fairly shortly after the IPO.