Hello Zubair,
Are these clients Managed / Unmanaged??
In case, UnManaged and you have scheduled these clients to download the Liveupdate at Night 10 pm, then they would connect to internet at 10.pm and they would get updates. (ofcourse the machines have to be ON)
Incase, they are Managed, it completely depends on the LiveUpdate Policy you have configured on the SEPM. Usually, the SEP clients would connect to the SEPM at 10.pm and check for updates at 10 pm. (ofcourse the machines have to be ON)
Few Articles to understand the LiveUpdate:
1) Symantec Endpoint Protection Manager - LiveUpdate - Policies explained
2) How client computers receive content updates
3) Configuring the LiveUpdate download schedule for client computers
Hope that answers!!