Crunch time means you don’t have a lot of time, you have a lot to do, mistakes can cost a lot, people depend on you, and likely you depend on other people.
People make mistakes. Also, sometimes you have to make decisions based on less information than you’d like. If people dwell on the mistakes or find out later that someone else could have made a better decision, they point fingers. Pointing fingers distracts from the task, takes time from productivity, and hurts morale.
My general advice

Don’t look for blame, but take responsibility for making things better to the extent you can

applies particularly well in crunch time. I’ll add more specific words that seem to come up in many crunch times. I say them when someone blames or second-guesses someone else (or themselves, including myself).

Yes, maybe we could have done that different given what we know now. But it’s done and we can’t change the past. For now, we still have to finish the project. If it’s important or we can learn from it, we’ll revisit what happened when we get the chance. We have to work with what we have, so let’s do what we can.

Especially in the frantic emotions of crunch time, people can easily get stuck pointing fingers, which can spiral out of control. People follow people who give them a way to move forward — people who lead. When you motivate people, including yourself, you lead. People want to follow people who lead, who help them get things done, and who know what to do in crunch time.
This statement addresses that something sub-optimal may have happened, but it points out we can’t change the past. It doesn’t say don’t point fingers, but achieves that goal anyway. I haven’t found telling people not to do something as effective in stopping that behavior as giving them something more productive to do that crowds out the unwanted behavior.
It addresses that we can return to something later if it helps and focuses people on getting things done.