The work before the moment determines how much thinking the moment requires.

How much you have to work out in the moment depends almost entirely on what you settled beforehand. If the decisions were made in advance, the moment only requires execution, which is manageable even under stress. If nothing was decided, you are thinking and performing at once, which is where most failures under pressure come from.

Before anything demanding, decide as much as you can in advance, the order, the fallback, what you will do if a particular thing goes wrong. Write it down. The aim is to leave the moment with as little thinking to do as possible.