Once your package arrives, there are a few things you can do to affect the ripening process of your fruit. If you wish, for example, to have some of the fruit ripen slower than the rest, you can place hard avocados in the fridge (or a cool dark place) for a day or two. This will not affect the quality of the fruit, but rather just give you an extra day or two to spread out the ripening of the order.
Alternatively, it is possible to significantly speed up the ripening process of the fruit. If you place green, hard avocados in a paper bag with a banana, banana peel or apple you can naturally accelerate the ripening. Put the items in a bag and put it in a warm place. Keep an eye on it!
Once you get the hang of it, choosing the perfect avocado at the perfect time is easy! The key with the Hass variety is to observe the color as well as the softness of the fruit. You'll want to see a change in color from green to a much darker green, nearly black. Additionally, take note of the firmness of the avocado as these colors change. It should be quite firm when green and will become increasingly soft as it ripens. Don't wait too long, though!
Hope this helps!