Tom,
The server command DISable SESSions will stop any "new" client scheduled
jobs from initiating contact with the server. Issue the ENable SESSions
command when you are ready to allow client activity again.
You'll want to keep the "DURation" parameter in the client scheduled entry
in mind. If you are using the default duration, which is one hour, and your
work takes over one hour then that backup will be missed.

SHC