Hmm well thats where your thermometer comes in handy lol. You dont have to let it sit overnight. You can just fill the bucket,put the condtioner in,throw the thermometer in and wait a bit. I usually make sure the tap is somewhat warm to my touch,so its usually around 78-80. But sometimes its higher so its good to check it. Then put water back in and then fishy. Lol. Its okay to have the new water temp off by 2 degrees higher or lower and put him in. They can handle that,just not more than 2 degrees either way.