Aha, here we go. You need Class A cultivars (receive pollen in morning) with Class B cultivars (distribute pollen in the morning). I don't know how you tell which is which. Typically growers put several of matching varieties in a grove.
@Coho Oooh, here's a good reference from UC Riverside.
M. L. Arpaia | University of California, Riverside A. E. Fetscher | University of California, Riverside R. Hofshi | Del Rey Avocado THE FLOWER Avocado productivity is influenced by many factors and involves many steps. The critical first step, however, is the process of pollination which leads to fertilization and fruit set. Pollination occurs when pollen is deposited on a receptive stigma. This poster describes some of the considerations pertaining to avocado pollination.