It is very important to check the moisture content of the fruit, as this is a great indicator:

Green skins- 76% & less
Dark skins – 78% or less

Avocados:
Fuerte/Pinkerton – February to March
Hass/Carmen – March, April, and May
Ryan – June, July, and August

In colder regions, harvesting may occur later, depending on the area and cultivar.