The shutdown time can be reduced by customizing the retries done by the Jobcheck if the machine is offline with the following configuration parameters under DSM > Software Delivery > Agent:
-Communication: Maximum number of initial retries (Unix) = 1
-Communication: Maximum number of retries (Unix) = 0
setting the initial retries parameter to 0 will prevent even the initial connection so no job will be executed even if the machine is online as the first connection will not be done.
Both parameters are set to 3 by default.
The following Idea has been raised at the Communities to avoid the Jobcheck at shutdown completely if the "run at shutdown" is not used in the environment: