From “ How Stuff Works.”
“After landing, the (Space Shuttle) crew goes through the shutdown procedures to power down the spacecraft. This process takes about 20 minutes. During this time, the orbiter is cooling and noxious gases, which were made during the heat of re-entry, blow away. Once the orbiter is powered down, the crew exits the vehicle. Ground crews are on-hand to begin servicing the orbiter.”
https://science.howstuffworks.com/space-shuttle7.htm