Are you using a "Managed Script" or a Distribution Package?
We started by using managed tasks but this was taking over 7 hours to shut down machines, so we switched to using a distributed package. This has been working fine and currently takes around 1 and half hours to send out (which is not ideal but the best we can get). We recently had an issue which caused the scheduler to lock and so when it was restarted the job began to run. So I have a further question. Is is possible to retrict a job, not just a recurring one, to run only within a certain time frame as it is the inventory scanner?