I was going to say it's not an hibiscus. Tell ya what, if you find some seeds, we will check that they are safe ones okay? The bush is called Rose of Sharon or Althea. The big dinner plate type ones that come up each year are called Hardy hibiscus. The the tropical ones are the ones which are not cold hardy, but have beautiful exotic looking blooms.
Very curious, where did you find that this is not safe to feed? I was under the impression that basically all parts of all hibiscus plants were good tortoise food, what did I miss?
Also this. http://www.illinoiswildflowers.info/weeds/plants/hour_flower.htm