I wonder what Sarah was doing when Abraham came running into the tent with this urgent instruction. Most likely she was in the midst of doing something and had planned her day. I do not imagine that her plans contained a clause saying, "In the event that the Lord and His angels should stop by...." Yet they did stop by, and she was to bake cakes. It was an ordinary task for an extraordinary moment.
I do not know Sarah's initial response when she was interrupted, but we are told that as they were enjoying the meal, she was listening in the tent door and was blessed by what she heard. It seems that Sarah was in no rush to resume her plans for the day. Whatever she had been doing could wait, for perhaps she perceived the hand of the Lord in the hindrance of her work.
I wonder how often upset plans are divine interruptions. Should we trust God with the interruptions more than we trust ourselves with our plans, what blessings would we hear and what laughter we would know within ourselves because of the astounding things that the Lord says? When plans are changed, keep an ear to the door; you just may hear the Lord.