I have never bothered to try this here in Florida or anywhere else, but perhaps you-all out in the deserts and semi-arid areas could try fogger/mister attachments on garden hoses, in very late afternoon through a couple of hours past sunset. Unless the female-stage-flower's stigmas are already drying out earlier than this--- you would be able to visually check this with a magnifier--- then protecting the viability of the pollen grains for a few hours should increase the efficacy of your hand-pollinations just before sunset.
Alternatively, you could tape the bottom of the flowers before they even open, and then remove the tape just momentarily for you to hand-pollinate, and then re-tape.
Sometimes, in very cool weather in the Spring, Roliinias flower synchronously: all male one eveing, all female next evening; this not only happens on an individual tree, but can happen on a whole row of trees. This issue goes away when the weather warms up.