As far as I know (and I have some success with crossing Hibiscus rosa-sinensis), the important thing is when the temps aren't too hot (below 90F) and crossing them in the mornings (when pollen is fresh).
If you want more specific advice, I can try to research this more.
Barb

Thank you so much for replying. I suppose my climate(Caribbean or Tropics) influenced the crosses more than I thought before.If it wouldn't be too much on your part, I wouldn't mind hearing your piece after research, as I've pretty much exhausted my Internet resources, having only received surface information(i.e. the method of crossing hibiscus plants).

Finally, I've achieved a cross. I crossed them around 9:00 am Thursday morning, and Saturday I realized the flower fell off and the base of the flower was swelling. I sincerely hope it keeps until it ripens. I guess the temperature really had a lot do with it, since it's cooler now. How soon should I cut the calyx so as to prevent it from harboring insects and fungus.