When the Linux machine is connected to the network it can take one minute to shutdown but if it's offline it can take several minutes.
CA Client Automation - All versions
Unix and Linux systems
When the system shuts down, a Jobcheck runs before stop CAF to connect to the Scalability Server to see if there are pending jobs marked to "run at shutdown" that is a feature only for Unix/Linux systems.
If the machine if offline, it does several retries every minute.