Well, I'm proceeding from the assumption that thoughtful review, which takes time, is desirable. If the situation is really that dire, then it's even more important that you ship product that works. Code review happens to be one of the, if not the most, effective ways to catch bugs and prevent disasters. It's a good idea to make the review process work for you, even and especially when the pressure is on.
It's not about humongous reviews being "inconvenient". A drop of thousands of lines of new code takes a long time to review thoroughly, whether the company is at risk of folding tomorrow or a stodgy enterprise with decades ahead of it. If you have to constrain review time - or ditch reviews altogether, why not? - you can, but there are consequences regardless.
I haven't worked in early startups, but I haven't only worked at large corporations either. I hope that most of us, most of the time, aren't less than a business day away from unemployment, and so there's usually time for code reviews. (If not, there's a lot of useless material about it!)
Without sarcasm, and potentially getting off-topic, I would like to hear stories about how a startup survived impending doom with heroic, fast shipping of product that set aside a lot of time-consuming processes. What were the most crucial steps to keep? How was the technical debt repaid?