I am by no means an expert in steam bending. I made a steam box pretty much like yours for a settee project last year.
I had to bend some 5/4″ elm into two 90 degrees bends.
The first attempts were not successful, even though I left the wood longer than the 1 hour per inch.
I found out that the temperature of the steam box was too low. So I wrapped my drain pipe (steam box) with 100 mm of insulation mat. That really helped a lot.
So may I suggest that you try to insulate your steam box? An effective and cheap insulation material is bubble wrap which can be found pretty cheap.
As far as I have understood, the wood will not take any harm in being left longer than the 1 hour per inch rule of thumb. It is supposedly intended as a minimum time, and that makes sense if you have to make a living out of building e.g. a boat.
So I would leave the wood in the steam box longer, say maybe half an hour.
Do you have a possibility of testing with some inferior wood before going on with the rose wood? That way you can perhaps gain some experience in placing the clamps etc.