Andy,
I do not know if this is what you want to do.
You can set up an admin schedule to lock the node before the schedule backup.
When the schedule backup complete, you can have another admin schedule to
unlock the node.
With the admin schedule there is a perameter called 'expiration.'
This specifies the date on which this schedule expires, in MM/DD/YYYY format. If you specify an expiration date, the schedule expires at 23:59:59 on the date you specify.
The lock node command is to prevent a client node from accessing the server. A locked client cannot perform any TSM operations, even if the operations are scheduled.
If there is another way, I would like to know my self.
Sias