If you really get pushed for time, to get the decision really quick, it's all going to depend on how well you've trained in the past. We just can't make a decision off the top of our heads when we aren't actually trained in what the situation is. Depending on how much experience you have you can make a good decision within less time under pressure. So experience is the key.
Take someone who is fixing automobiles for over thirty years, somebody comes in "Hey, please, can you fix this really quick?" He will probably be able to do it as quick as possible as he has thirty years experience. A brand new, young mechanic who is just begun training would probably go, "Oh, uh". Yeah, so experience is the key to be able to make good decisions in less time.
Now, if you've thrown into a position and you have to make a decision and you don't have the experience, it's a good idea to tell people. Tell the people who are pressuring you.
A lot of people come to us and talk about how at work there is never enough time, the bosses want this, the bosses want that. They often confess to us that they really did not understand everything that the boss wanted to be done but they never actually said to the boss, "I don't understand" because they were afraid of what the boss would think of them. But look at it this way, either you tell the boss you don't understand so the boss will explain more or else you try on your own and you may make a big mistake and the boss thinks you are a total dill. So actually saying to the boss, "Look, I don't know, I'm not sure" is a better way of thinking, it's a better approach when you get thrown into something that's over your head.