Re: how/when to repot hibiscus
Your hibiscus sounds really beautiful!
If it were mine, I'd wait on re-potting until it's done flowering. or you might lose ALL the buds. If it's wilting without getting that single glass of water each day, and it is severely pot-bound, I doubt it's being over-watered.
If you can lift the whole plant out of the pot a ways, you should be able to see the roots, if it's more roots then soil which wrap around and around inside the pot, drying out very quickly only a day, or two after watering, that would be considered severely root-bound.
You might not be watering it enough if it is really root-bound. Then you'll need to soak the soil with more then just a glass of water, making sure the entire root-ball gets wet. Submerging the entire pot until water flows in over the rim is another way if hydrating a very thirsty dry plant. Keep it under the water until the soil stops bubbling, replacing any soil that floats away after lifting it out.
When you do re-pot, only go up one pot size larger. You'll want an inch, or two, of root-ball room inside the new pot is all.