Hi,
i am not sure about the day/night temperature drop in the habitats. I think, at least during winter, it can get quite cold, i would not even be surprised if the temperatures can go down as low as 0°C. I can assure you, that the weather on the Table Mountain can change within minutes from warm sunshine to cold fog. In cultivation, the plants do not need a night/day drop and will do fine with normal temperature. In my opinion, they benefit from a colder winter, though.
Drosera admirabilis sp. "floating" is growing in shallow flowing water. The water level is about 2-3 cm. The plants are not really floating, as they are still fixed to the soil. They just form a stem to put the rosettes over the water. We also found examples, that have grown "normaly".
regards,
Christian