This is something that a friend of mine who worked shift hours do Maybe you can try if you think is ok.

He suntan his ranchu between 8am-12pm whenever he's home during this period of time. He put one ranchu in the white basin (with an airstone) and leave it in a place where there are sunlight. After the suntan, the ranchu is slowly introduced back into the main tub indoor. The water in the basin is usually discarded.

Good or bad, I dun know. I personally find it too much of a hassle.