It is best to drain fluids when they are at normal operating temps, immediately after riding. There are a couple reasons for this, the first and most important being that the oil holds contaminants in suspension during operation but will allow junk to settle out as it sits. You want to drain out the maximum amount of the contaminants. Another reason is that warm or hot fluids will drain quicker and more completely.
Be careful to protect your hands/skin, as hot oil can cause scald injuries. I personally ride the bike for about ten miles to get everything up to operating temperature, then pull into the garage and let the bike idle on the jiffy stand for a couple minutes (to let the oil pump move as much oil as possible to the tank), shut the bike down and immediately remove the drain plugs and let the fluids drain. I wait awhile to remove the oil filter, since removing it when hot usually results in a gusher that makes quite a mess no matter what device or method I use to catch the oil.
Jerry