Hello
When you create a new client, you just create an entry in table T000 and it is possible to login.
All the customizing tables for that client are empty, so no country code or time zone is defined.
Before creating users you need to make a client copy from client 000 in that client using the kernel hard coded user SAP*.
Regards
550894 CC-ADMIN: Setting up a new client
Use SCCL (local client copy) in the target client, client 000 as a source client & SAP_CUST profile.