Each flower opens first as a female and then the next day as a male. On top of this unusual feature, there are two types of avocado trees with different timing of the flowers: A-type trees open their female flowers in the morning and these flowers reopen as males in the afternoon. B-type trees open their female flowers in the afternoon and then their male flowers the following morning. Since fruiting requires cross-pollination, it helps to have both phases. (UCLA Agriculture avocado information)
My parents have three avocado trees in their backyard in Florida. One never bears any fruit. The other two are large trees that bear delicious harvests. Maybe the trees are different phases?