How to default Time zone for iSupplier Users

Dear Experts,

We have requirement that our Client Time Zone is changed from Server Time zone. Server time zone is used as Calcutta and Client time zone is used as Karachi time zone.

Now for iSupplier user if user is of Karachi than how we can default the client time zone profile on it? As in iSupplier users are creating automatically, so need to know how we can default Client time for the newly created user?

Thanks in Advance..........