This technique can be done in 1-2 minutes, or half an hour, depending on how much time you have and how much you need to re-centre. It can be used at any time, like while you’re brushing your teeth or waiting for the kettle to boil.
However, it is a very helpful response to difficult emotions or worries. When we feel strong unpleasant emotions we tend to try and solve them or get rid of them immediately. Doing a 3-minute breathing space in these moments will help us to slow down and stay calm, present and aware- the best way to be for making rational and helpful decisions.
This exercise is often explained with an hour glass metaphor: Your attention is the sand. It starts broad at the top collecting into one place. Then it narrows as much as possible, and then expands again, settling in a different way.