The temperature of the ashes will cool down gradually. It can take up to several hours for the ashes to reach room temperature. Depending on how much heat was put into the ash, it may be still warm enough to start a fire later on. If you are concerned that the ashes have cooled down too much, you can place them in a metal container and set it on top of a stove to heat up. Be sure to use caution when handling hot ashes.