There are multiple ways in which client get updates...
Client checks the server based on heartbeat... So you can set the heartbeat interval based on ur need. There is no schedule option available for this.
You can use internal liveupdate server to update clients.. You have a option to schedule it. Its available under liveupdate policy....
Work around for schedule updates....(Give a try.. it should work)
Set any non existing ip as a GUP. Now when a client check in with the server its get the GUP info and tried to contact it. Sicne you have configured non existing GUP it wont download the updates.
Now you have to install and configure a liveupdate server and assign it in liveupdate policy. You can schedule the update as per your need...
Now clients will get update as per the schedule..
REF:
https://www-secure.symantec.com/connect/articles/installation-and-configuration-lua