Your best chance of getting hibiscus seed requires fresh pollen, that gold powdery substance, and fresh, receptive stigma pads that will allow that pollen to fertilize the ovules within the ovary at the base of the bloom. When this happens, conception may occur. Some hybridizers have had success late in the afternoon and some when temperatures were in the mid-90s. Still, working early in the morning when the pollen has just been released by the pollen sacs and when the pads are fresh on a newly opened flower seems to increase the rate of success. That pollen needs time to make the connection to the ovary at the base of the bloom.
High humidity slows the drying of the pollen and the pads.
Some varieties produce little pollen and some pollen may be more potent than other pollen. Tranferring pollen to the pads can be done in different ways. Some hybridizers use tweezers or surgical forceps to remove the pollen sacs from the style. Some use a soft brush to remove the pollen and apply to the pads. After the pollen has been applied, it's wise to carefully wrap some sort of label around the stem of the flower with the identity of the pollen parent, the date of pollnation, etc.