Have you ever gone to buy an avocado and all you can find are rock hard, under-ripe avocados that look like they won't be ripe for a week? This happens to me all the time and I usually want to use the avocado within a day or two.
There is a trick to make avocado's ripen faster. I can't guarantee how quickly it will happen, however, if you place the avocado in a brown paper bag with a banana, apple or tomato, the avocado will ripen faster. True story. Just remember to store the bag at room temperature out of direct sunlight.