I'm a little behind on things... the 'Blue River II' X grandiflorus hibiscus hybrid opened a while ago and it's a big, light pink with darker eyezone just as expected. First picture I took with my phone was the second bloom open. The second picture was this morning. It IS lightly fragrant - maybe only slightly less so than it's pollen parent. It's also nocturnal in habit like grandiflorus. I finally also detected a little bit of scent from freshly opening flowers of 'Moy Grande' (which is also supposed to be half grandiflorus). My hybrid has a little more scent and is more strongly nocturnal. See the collage of pictures showing my hybrid fairly wide open, 'Moy Grande' bud partially open and 'Blue River II' bud not open at all yet. The downside of this early opening is that they close earliest too. See 'Blue River II' still has a previous day's flower open at 10:00 PM. Maybe some of the F2 will open early and stay open.
Here's another named hibiscus that has beautiful flowers. Unfortunately the sawfly "caterpillars" love to munch the leaves too. I'm putting 'Moy Grande' pollen on it, to try to get more sawfly resistance and keep the big red flowers.
The last two pictures are of 'Moy Grande' - one of my all time favorite hibiscus. Huge flowers, good foliage and a little bit of scent when first opening.