I am making the assumption you are talking about Tropical hibiscuses. As long as it doesn't frost on them, you are OK. Now everyone says the freezing point is 32*F but you often have frost when the official temps are within a few degrees plus or minus. Anytime the predicted temp goes below 40*F, I recommend bring them inside.

Sounds right to me. I brought my annual hibiscus inside when they said the frost was coming a couple weeks ago. I have had this plant for two years and it doubled in size. It is near a sunny window and is still blooming! It will loose its leaves here soon and I will keep it inside until Spring.

Do you know if this plant produces seed? How would I harvest them? I don't ever see anything that resembles seed pods.

Thanks.

They don't self seed. You'd have to get another or at least get your hands on the flower from another.
Here's a link describing how it's done.
Barb

Here is a link that might be useful: Queen of the Tropics page on seeds

Thank you so much for that information. My hibiscus is doing great and now I know NOT to look for a seed pod to grow on it. I will just continue to take it inside for the winter months and see how long I can keep it alive.