The problem with Impatiens in hot places is that they drink tons of water, I plant mine in full sun and here it can get as hot and muggy as in Fla., they need twice a day watering ( early in the morning and at mid day ). They should benefit from the "cooler" ( in figurative sense )winter temperatures and it´s preciselly at this time of the year when they begin looking much better than during the spring and summer. They bloom more with bigger blooms.

I hear in Flordia that it now the best time to plant them. Here in the California Sacramento valley we grow them from early spring to fall sometimes they will survive. Our temps can reach in the 100s but very dry and they do great. I guess they dont like humid heat. You could try niamniamensis it takes my heat really well it might do ok for you as well. Maybe even Impatiens grandis which is very rare. It flowers around Xmas time, big plant wiht big flowers.