Pitcher method

CMH

Can someone explain the pitcher method exactly?

For instance, I currently have 4 bottles prepped for baby and 3 oz waiting to be mixed with another pump session to create enough for 1 bottle.

If I were to use the pitcher method, would I pour that plus my next pump in one container for ___ amount of time then pour that into bottles or bags then start over? What if I don't make enough in that time to supply enough bottles for my baby?